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• How to get type of TKey and TValue given a Dictionary<TKey,TValue> type

  - by harsha

  I want to get type of TKey and TValue given a Dictionary<TKey,TValue> type. eg. If type is Dictionary<Int32,String> I want to know how to get keyType = typeof(Int32) and valueType = typeof(String)

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• ConcurrentDictionary<TKey,TValue> used with Lazy<T>

  - by Reed

  In a recent thread on the MSDN forum for the TPL, Stephen Toub suggested mixing ConcurrentDictionary<T,U> with Lazy<T>.  This provides a fantastic model for creating a thread safe dictionary of values where the construction of the value type is expensive.  This is an incredibly useful pattern for many operations, such as value caches. The ConcurrentDictionary<TKey, TValue> class was added in .NET 4, and provides a thread-safe, lock free collection of key value pairs.  While this is a fantastic replacement for Dictionary<TKey, TValue>, it has a potential flaw when used with values where construction of the value class is expensive. The typical way this is used is to call a method such as GetOrAdd to fetch or add a value to the dictionary.  It handles all of the thread safety for you, but as a result, if two threads call this simultaneously, two instances of TValue can easily be constructed. If TValue is very expensive to construct, or worse, has side effects if constructed too often, this is less than desirable.  While you can easily work around this with locking, Stephen Toub provided a very clever alternative – using Lazy<TValue> as the value in the dictionary instead. This looks like the following.  Instead of calling: MyValue value = dictionary.GetOrAdd( key, () => new MyValue(key)); .csharpcode, .csharpcode pre { font-size: small; color: black; font-family: consolas, "Courier New", courier, monospace; background-color: #ffffff; /*white-space: pre;*/ } .csharpcode pre { margin: 0em; } .csharpcode .rem { color: #008000; } .csharpcode .kwrd { color: #0000ff; } .csharpcode .str { color: #006080; } .csharpcode .op { color: #0000c0; } .csharpcode .preproc { color: #cc6633; } .csharpcode .asp { background-color: #ffff00; } .csharpcode .html { color: #800000; } .csharpcode .attr { color: #ff0000; } .csharpcode .alt { background-color: #f4f4f4; width: 100%; margin: 0em; } .csharpcode .lnum { color: #606060; } We would instead use a ConcurrentDictionary<TKey, Lazy<TValue>>, and write: MyValue value = dictionary.GetOrAdd( key, () => new Lazy<MyValue>( () => new MyValue(key))) .Value; This simple change dramatically changes how the operation works.  Now, if two threads call this simultaneously, instead of constructing two MyValue instances, we construct two Lazy<MyValue> instances. However, the Lazy<T> class is very cheap to construct.  Unlike “MyValue”, we can safely afford to construct this twice and “throw away” one of the instances. We then call Lazy<T>.Value at the end to fetch our “MyValue” instance.  At this point, GetOrAdd will always return the same instance of Lazy<MyValue>.  Since Lazy<T> doesn’t construct the MyValue instance until requested, the actual MyClass instance returned is only constructed once.

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• RTTI Delphi Create as TValue an n-dimensional matrix.

  - by user558126

  Good day, I had tried to make recurrent function to return a TValue as a n-dimensional. matrix(2D, 3D, 4D...) for example, this procedure will show a n-dimensional matrix(it will list all elements from a n-dimensional matrix as TValue variable): Procedure Show(X:TValue); var i:integer; begin if x.IsArray then begin for i:=0 to x.GetArrayLength-1 do show(x.GetArrayElement(i)); writeln; end else write(x.ToString,' '); end; I don't understand how to create a function to create from a TValue an n-dimensional matrix. For example i need a Function CreateDynArray(Dimensions:array of integer; Kind:TTypeKind):TValue; and the function will return a TValue which is a dynamic array how contain the dimenssions for example: Return=CreateDynArray([2,3],tkInteger); will return a TValue as tkDynArray and if i will show(Return) will list 0 0 0 0 0 0 Thank you very much, and have a nice day!

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• C#/.NET Little Wonders: Using &lsquo;default&rsquo; to Get Default Values

  - by James Michael Hare

  Once again, in this series of posts I look at the parts of the .NET Framework that may seem trivial, but can help improve your code by making it easier to write and maintain. The index of all my past little wonders posts can be found here. Today’s little wonder is another of those small items that can help a lot in certain situations, especially when writing generics.  In particular, it is useful in determining what the default value of a given type would be. The Problem: what’s the default value for a generic type? There comes a time when you’re writing generic code where you may want to set an item of a given generic type.  Seems simple enough, right?  We’ll let’s see! Let’s say we want to query a Dictionary<TKey, TValue> for a given key and get back the value, but if the key doesn’t exist, we’d like a default value instead of throwing an exception. So, for example, we might have a the following dictionary defined: 1: var lookup = new Dictionary<int, string> 2: { 3: { 1, "Apple" }, 4: { 2, "Orange" }, 5: { 3, "Banana" }, 6: { 4, "Pear" }, 7: { 9, "Peach" } 8: }; And using those definitions, perhaps we want to do something like this: 1: // assume a default 2: string value = "Unknown"; 3:  4: // if the item exists in dictionary, get its value 5: if (lookup.ContainsKey(5)) 6: { 7: value = lookup[5]; 8: } But that’s inefficient, because then we’re double-hashing (once for ContainsKey() and once for the indexer).  Well, to avoid the double-hashing, we could use TryGetValue() instead: 1: string value; 2:  3: // if key exists, value will be put in value, if not default it 4: if (!lookup.TryGetValue(5, out value)) 5: { 6: value = "Unknown"; 7: } But the “flow” of using of TryGetValue() can get clunky at times when you just want to assign either the value or a default to a variable.  Essentially it’s 3-ish lines (depending on formatting) for 1 assignment.  So perhaps instead we’d like to write an extension method to support a cleaner interface that will return a default if the item isn’t found: 1: public static class DictionaryExtensions 2: { 3: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 4: TKey key, TValue defaultIfNotFound) 5: { 6: TValue value; 7:  8: // value will be the result or the default for TValue 9: if (!dict.TryGetValue(key, out value)) 10: { 11: value = defaultIfNotFound; 12: } 13:  14: return value; 15: } 16: } 17:  So this creates an extension method on Dictionary<TKey, TValue> that will attempt to get a value using the given key, and will return the defaultIfNotFound as a stand-in if the key does not exist. This code compiles, fine, but what if we would like to go one step further and allow them to specify a default if not found, or accept the default for the type?  Obviously, we could overload the method to take the default or not, but that would be duplicated code and a bit heavy for just specifying a default.  It seems reasonable that we could set the not found value to be either the default for the type, or the specified value. So what if we defaulted the type to null? 1: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 2: TKey key, TValue defaultIfNotFound = null) // ... No, this won’t work, because only reference types (and Nullable<T> wrapped types due to syntactical sugar) can be assigned to null.  So what about a calling parameterless constructor? 1: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 2: TKey key, TValue defaultIfNotFound = new TValue()) // ... No, this won’t work either for several reasons.  First, we’d expect a reference type to return null, not an “empty” instance.  Secondly, not all reference types have a parameter-less constructor (string for example does not).  And finally, a constructor cannot be determined at compile-time, while default values can. The Solution: default(T) – returns the default value for type T Many of us know the default keyword for its uses in switch statements as the default case.  But it has another use as well: it can return us the default value for a given type.  And since it generates the same defaults that default field initialization uses, it can be determined at compile-time as well. For example: 1: var x = default(int); // x is 0 2:  3: var y = default(bool); // y is false 4:  5: var z = default(string); // z is null 6:  7: var t = default(TimeSpan); // t is a TimeSpan with Ticks == 0 8:  9: var n = default(int?); // n is a Nullable<int> with HasValue == false Notice that for numeric types the default is 0, and for reference types the default is null.  In addition, for struct types, the value is a default-constructed struct – which simply means a struct where every field has their default value (hence 0 Ticks for TimeSpan, etc.). So using this, we could modify our code to this: 1: public static class DictionaryExtensions 2: { 3: public static TValue GetValueOrDefault<TKey, TValue>(this Dictionary<TKey, TValue> dict, 4: TKey key, TValue defaultIfNotFound = default(TValue)) 5: { 6: TValue value; 7:  8: // value will be the result or the default for TValue 9: if (!dict.TryGetValue(key, out value)) 10: { 11: value = defaultIfNotFound; 12: } 13:  14: return value; 15: } 16: } Now, if defaultIfNotFound is unspecified, it will use default(TValue) which will be the default value for whatever value type the dictionary holds.  So let’s consider how we could use this: 1: lookup.GetValueOrDefault(1); // returns “Apple” 2:  3: lookup.GetValueOrDefault(5); // returns null 4:  5: lookup.GetValueOrDefault(5, “Unknown”); // returns “Unknown” 6:  Again, do not confuse a parameter-less constructor with the default value for a type.  Remember that the default value for any type is the compile-time default for any instance of that type (0 for numeric, false for bool, null for reference types, and struct will all default fields for struct).  Consider the difference: 1: // both zero 2: int i1 = default(int); 3: int i2 = new int(); 4:  5: // both “zeroed” structs 6: var dt1 = default(DateTime); 7: var dt2 = new DateTime(); 8:  9: // sb1 is null, sb2 is an “empty” string builder 10: var sb1 = default(StringBuilder()); 11: var sb2 = new StringBuilder(); So in the above code, notice that the value types all resolve the same whether using default or parameter-less construction.  This is because a value type is never null (even Nullable<T> wrapped types are never “null” in a reference sense), they will just by default contain fields with all default values. However, for reference types, the default is null and not a constructed instance.  Also it should be noted that not all classes have parameter-less constructors (string, for instance, doesn’t have one – and doesn’t need one). Summary Whenever you need to get the default value for a type, especially a generic type, consider using the default keyword.  This handy word will give you the default value for the given type at compile-time, which can then be used for initialization, optional parameters, etc. Technorati Tags: C#,CSharp,.NET,Little Wonders,default

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• Accessing data stored in another unit Delphi

  - by Hendriksen123

  In Unit2 of my program i have the following code: TValue = Record NewValue, OldValue, SavedValue : Double; end; TData = Class(TObject) Public EconomicGrowth : TValue; Inflation : TValue; Unemployment : TValue; CurrentAccountPosition : TValue; AggregateSupply : TValue; AggregateDemand : TValue; ADGovernmentSpending : TValue; ADConsumption : TValue; ADInvestment : TValue; ADNetExports : TValue; OverallTaxation : TValue; GovernmentSpending : TValue; InterestRates : TValue; IncomeTax : TValue; Benefits : TValue; TrainingEducationSpending : TValue; End; I then declare Data : TData in the Var. when i try to do the following however in Unit1: ShowMessage(FloatToStr(Unit2.Data.Inflation.SavedValue)); I get an EAccessViolation message. Is there any way to access the data stored in 'Data' from Unit1 without getting errors?

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• Delphi interface cast using TValue

  - by conciliator

  I've recently experimented extensively with interfaces and D2010 RTTI. I don't know at runtime the actual type of the interface; although I will have access to it's qualified name using a string. Consider the following: program rtti_sb_1; {$APPTYPE CONSOLE} uses SysUtils, Rtti, TypInfo, mynamespace in 'mynamespace.pas'; var ctx: TRttiContext; InterfaceType: TRttiType; Method: TRttiMethod; ActualParentInstance: IParent; ChildInterfaceValue: TValue; ParentInterfaceValue: TValue; begin ctx := TRttiContext.Create; // Instantiation ActualParentInstance := TChild.Create as IParent; {$define WORKAROUND} {$ifdef WORKAROUND} InterfaceType := ctx.GetType(TypeInfo(IParent)); InterfaceType := ctx.GetType(TypeInfo(IChild)); {$endif} // Fetch interface type InterfaceType := ctx.FindType('mynamespace.IParent'); // This cast is OK and ChildMethod is executed (ActualParentInstance as IChild).ChildMethod(100); // Create a TValue holding the interface TValue.Make(@ActualParentInstance, InterfaceType.Handle, ParentInterfaceValue); InterfaceType := ctx.FindType('mynamespace.IChild'); // This cast doesn't work if ParentInterfaceValue.TryCast(InterfaceType.Handle, ChildInterfaceValue) then begin Method := InterfaceType.GetMethod('ChildMethod'); if (Method <> nil) then begin Method.Invoke(ChildInterfaceValue, [100]); end; end; ReadLn; end. The contents of mynamespace.pas is as follows: {$M+} IParent = interface ['{2375F59E-D432-4D7D-8D62-768F4225FFD1}'] procedure ParentMethod(const Id: integer); end; {$M-} IChild = interface(IParent) ['{6F89487E-5BB7-42FC-A760-38DA2329E0C5}'] procedure ChildMethod(const Id: integer); end; TParent = class(TInterfacedObject, IParent) public procedure ParentMethod(const Id: integer); end; TChild = class(TParent, IChild) public procedure ChildMethod(const Id: integer); end; For completeness, the implementation goes as procedure TParent.ParentMethod(const Id: integer); begin WriteLn('ParentMethod executed. Id is ' + IntToStr(Id)); end; procedure TChild.ChildMethod(const Id: integer); begin WriteLn('ChildMethod executed. Id is ' + IntToStr(Id)); end; The reason for {$define WORKAROUND} may be found in this post. Question: is there any way for me to make the desired type cast using RTTI? In other words: is there a way for me to invoke IChild.ChildMethod from knowing 1) the qualified name of IChild as a string, and 2) a reference to the TChild instance as a IParent interface? (After all, the hard-coded cast works fine. Is this even possible?) Thanks!

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• RTTI Dynamic array TValue Delphi 2010

  - by user558126

  Hello I have a question. I am a newbie with Run Time Type Information from Delphi 2010. I need to set length to a dynamic array into a TValue. You can see the code. Type TMyArray = array of integer; TMyClass = class publihed function Do:TMyArray; end; function TMyClass.Do:TMyArray; begin SetLength(Result,5); for i:=0 to 4 Result[i]=3; end; ....... ....... ...... y:TValue; Param:array of TValue; ......... y=Methods[i].Invoke(Obj,Param);//delphi give me a DynArray type kind, is working, Param works to any functions. if Method[i].ReturnType.TypeKind = tkDynArray then//is working... begin I want to set length for y to 10000//i don't know how to write. end; I don't like Generics Collections.

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• Rtti data manipulation and consistency in Delphi 2010

  - by Coco

  Has anyone an idea, how I can make TValue using a reference to the original data? In my serialization project, I use (as suggested in XML-Serialization) a generic serializer which stores TValues in an internal tree-structure (similar to the MemberMap in the example). This member-tree should also be used to create a dynamic setup form and manipulate the data. My idea was to define a property for the Data: TDataModel <T> = class {...} private FData : TValue; function GetData : T; procedure SetData (Value : T); public property Data : T read GetData write SetData; end; The implementation of the GetData, SetData Methods: procedure TDataModel <T>.SetData (Value : T); begin FData := TValue.From <T> (Value); end; procedure TDataModel <T>.GetData : T; begin Result := FData.AsType <T>; end; Unfortunately, the TValue.From method always makes a copy of the original data. So whenever the application makes changes to the data, the DataModel is not updated and vice versa if I change my DataModel in a dynamic form, the original data is not affected. Sure I could always use the Data property before and after changing anything, but as I use lot of Rtti inside my DataModel, I do not realy want to do this anytime. Perhaps someone has a better suggestion?

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• Creating Property Set Expression Trees In A Developer Friendly Way

  - by Paulo Morgado

  In a previous post I showed how to create expression trees to set properties on an object. The way I did it was not very developer friendly. It involved explicitly creating the necessary expressions because the compiler won’t generate expression trees with property or field set expressions. Recently someone contacted me the help develop some kind of command pattern framework that used developer friendly lambdas to generate property set expression trees. Simply putting, given this entity class: public class Person { public string Name { get; set; } } The person in question wanted to write code like this: var et = Set((Person p) => p.Name = "me"); Where et is the expression tree that represents the property assignment. So, if we can’t do this, let’s try the next best thing that is splitting retrieving the property information from the retrieving the value to assign o the property: var et = Set((Person p) => p.Name, () => "me"); And this is something that the compiler can handle. The implementation of Set receives an expression to retrieve the property information from and another expression the retrieve the value to assign to the property: public static Expression<Action<TEntity>> Set<TEntity, TValue>( Expression<Func<TEntity, TValue>> propertyGetExpression, Expression<Func<TValue>> valueExpression) The implementation of this method gets the property information form the body of the property get expression (propertyGetExpression) and the value expression (valueExpression) to build an assign expression and builds a lambda expression using the same parameter of the property get expression as its parameter: public static Expression<Action<TEntity>> Set<TEntity, TValue>( Expression<Func<TEntity, TValue>> propertyGetExpression, Expression<Func<TValue>> valueExpression) { var entityParameterExpression = (ParameterExpression)(((MemberExpression)(propertyGetExpression.Body)).Expression); return Expression.Lambda<Action<TEntity>>( Expression.Assign(propertyGetExpression.Body, valueExpression.Body), entityParameterExpression); } And now we can use the expression to translate to another context or just compile and use it: var et = Set((Person p) => p.Name, () => name); Console.WriteLine(person.Name); // Prints: p => (p.Name = “me”) var d = et.Compile(); d(person); Console.WriteLine(person.Name); // Prints: me It can even support closures: var et = Set((Person p) => p.Name, () => name); Console.WriteLine(person.Name); // Prints: p => (p.Name = value(<>c__DisplayClass0).name) var d = et.Compile(); name = "me"; d(person); Console.WriteLine(person.Name); // Prints: me name = "you"; d(person); Console.WriteLine(person.Name); // Prints: you Not so useful in the intended scenario (but still possible) is building an expression tree that receives the value to assign to the property as a parameter: public static Expression<Action<TEntity, TValue>> Set<TEntity, TValue>(Expression<Func<TEntity, TValue>> propertyGetExpression) { var entityParameterExpression = (ParameterExpression)(((MemberExpression)(propertyGetExpression.Body)).Expression); var valueParameterExpression = Expression.Parameter(typeof(TValue)); return Expression.Lambda<Action<TEntity, TValue>>( Expression.Assign(propertyGetExpression.Body, valueParameterExpression), entityParameterExpression, valueParameterExpression); } This new expression can be used like this: var et = Set((Person p) => p.Name); Console.WriteLine(person.Name); // Prints: (p, Param_0) => (p.Name = Param_0) var d = et.Compile(); d(person, "me"); Console.WriteLine(person.Name); // Prints: me d(person, "you"); Console.WriteLine(person.Name); // Prints: you The only caveat is that we need to be able to write code to read the property in order to write to it.

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• An Xml Serializable PropertyBag Dictionary Class for .NET

  - by Rick Strahl

  I don't know about you but I frequently need property bags in my applications to store and possibly cache arbitrary data. Dictionary<T,V> works well for this although I always seem to be hunting for a more specific generic type that provides a string key based dictionary. There's string dictionary, but it only works with strings. There's Hashset<T> but it uses the actual values as keys. In most key value pair situations for me string is key value to work off. Dictionary<T,V> works well enough, but there are some issues with serialization of dictionaries in .NET. The .NET framework doesn't do well serializing IDictionary objects out of the box. The XmlSerializer doesn't support serialization of IDictionary via it's default serialization, and while the DataContractSerializer does support IDictionary serialization it produces some pretty atrocious XML. What doesn't work? First off Dictionary serialization with the Xml Serializer doesn't work so the following fails: [TestMethod] public void DictionaryXmlSerializerTest() { var bag = new Dictionary<string, object>(); bag.Add("key", "Value"); bag.Add("Key2", 100.10M); bag.Add("Key3", Guid.NewGuid()); bag.Add("Key4", DateTime.Now); bag.Add("Key5", true); bag.Add("Key7", new byte[3] { 42, 45, 66 }); TestContext.WriteLine(this.ToXml(bag)); } public string ToXml(object obj) { if (obj == null) return null; StringWriter sw = new StringWriter(); XmlSerializer ser = new XmlSerializer(obj.GetType()); ser.Serialize(sw, obj); return sw.ToString(); } The error you get with this is: System.NotSupportedException: The type System.Collections.Generic.Dictionary`2[[System.String, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Object, mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]] is not supported because it implements IDictionary. Got it! BTW, the same is true with binary serialization. Running the same code above against the DataContractSerializer does work: [TestMethod] public void DictionaryDataContextSerializerTest() { var bag = new Dictionary<string, object>(); bag.Add("key", "Value"); bag.Add("Key2", 100.10M); bag.Add("Key3", Guid.NewGuid()); bag.Add("Key4", DateTime.Now); bag.Add("Key5", true); bag.Add("Key7", new byte[3] { 42, 45, 66 }); TestContext.WriteLine(this.ToXmlDcs(bag)); } public string ToXmlDcs(object value, bool throwExceptions = false) { var ser = new DataContractSerializer(value.GetType(), null, int.MaxValue, true, false, null); MemoryStream ms = new MemoryStream(); ser.WriteObject(ms, value); return Encoding.UTF8.GetString(ms.ToArray(), 0, (int)ms.Length); } This DOES work but produces some pretty heinous XML (formatted with line breaks and indentation here): <ArrayOfKeyValueOfstringanyType xmlns="http://schemas.microsoft.com/2003/10/Serialization/Arrays" xmlns:i="http://www.w3.org/2001/XMLSchema-instance"> <KeyValueOfstringanyType> <Key>key</Key> <Value i:type="a:string" xmlns:a="http://www.w3.org/2001/XMLSchema">Value</Value> </KeyValueOfstringanyType> <KeyValueOfstringanyType> <Key>Key2</Key> <Value i:type="a:decimal" xmlns:a="http://www.w3.org/2001/XMLSchema">100.10</Value> </KeyValueOfstringanyType> <KeyValueOfstringanyType> <Key>Key3</Key> <Value i:type="a:guid" xmlns:a="http://schemas.microsoft.com/2003/10/Serialization/">2cd46d2a-a636-4af4-979b-e834d39b6d37</Value> </KeyValueOfstringanyType> <KeyValueOfstringanyType> <Key>Key4</Key> <Value i:type="a:dateTime" xmlns:a="http://www.w3.org/2001/XMLSchema">2011-09-19T17:17:05.4406999-07:00</Value> </KeyValueOfstringanyType> <KeyValueOfstringanyType> <Key>Key5</Key> <Value i:type="a:boolean" xmlns:a="http://www.w3.org/2001/XMLSchema">true</Value> </KeyValueOfstringanyType> <KeyValueOfstringanyType> <Key>Key7</Key> <Value i:type="a:base64Binary" xmlns:a="http://www.w3.org/2001/XMLSchema">Ki1C</Value> </KeyValueOfstringanyType> </ArrayOfKeyValueOfstringanyType> Ouch! That seriously hurts the eye! :-) Worse though it's extremely verbose with all those repetitive namespace declarations. It's good to know that it works in a pinch, but for a human readable/editable solution or something lightweight to store in a database it's not quite ideal. Why should I care? As a little background, in one of my applications I have a need for a flexible property bag that is used on a free form database field on an otherwise static entity. Basically what I have is a standard database record to which arbitrary properties can be added in an XML based string field. I intend to expose those arbitrary properties as a collection from field data stored in XML. The concept is pretty simple: When loading write the data to the collection, when the data is saved serialize the data into an XML string and store it into the database. When reading the data pick up the XML and if the collection on the entity is accessed automatically deserialize the XML into the Dictionary. (I'll talk more about this in another post). While the DataContext Serializer would work, it's verbosity is problematic both for size of the generated XML strings and the fact that users can manually edit this XML based property data in an advanced mode. A clean(er) layout certainly would be preferable and more user friendly. Custom XMLSerialization with a PropertyBag Class So… after a bunch of experimentation with different serialization formats I decided to create a custom PropertyBag class that provides for a serializable Dictionary. It's basically a custom Dictionary<TType,TValue> implementation with the keys always set as string keys. The result are PropertyBag<TValue> and PropertyBag (which defaults to the object type for values). The PropertyBag<TType> and PropertyBag classes provide these features: Subclassed from Dictionary<T,V> Implements IXmlSerializable with a cleanish XML format ToXml() and FromXml() methods to export and import to and from XML strings Static CreateFromXml() method to create an instance It's simple enough as it's merely a Dictionary<string,object> subclass but that supports serialization to a - what I think at least - cleaner XML format. The class is super simple to use: [TestMethod] public void PropertyBagTwoWayObjectSerializationTest() { var bag = new PropertyBag(); bag.Add("key", "Value"); bag.Add("Key2", 100.10M); bag.Add("Key3", Guid.NewGuid()); bag.Add("Key4", DateTime.Now); bag.Add("Key5", true); bag.Add("Key7", new byte[3] { 42,45,66 } ); bag.Add("Key8", null); bag.Add("Key9", new ComplexObject() { Name = "Rick", Entered = DateTime.Now, Count = 10 }); string xml = bag.ToXml(); TestContext.WriteLine(bag.ToXml()); bag.Clear(); bag.FromXml(xml); Assert.IsTrue(bag["key"] as string == "Value"); Assert.IsInstanceOfType( bag["Key3"], typeof(Guid)); Assert.IsNull(bag["Key8"]); //Assert.IsNull(bag["Key10"]); Assert.IsInstanceOfType(bag["Key9"], typeof(ComplexObject)); } This uses the PropertyBag class which uses a PropertyBag<string,object> - which means it returns untyped values of type object. I suspect for me this will be the most common scenario as I'd want to store arbitrary values in the PropertyBag rather than one specific type. The same code with a strongly typed PropertyBag<decimal> looks like this: [TestMethod] public void PropertyBagTwoWayValueTypeSerializationTest() { var bag = new PropertyBag<decimal>(); bag.Add("key", 10M); bag.Add("Key1", 100.10M); bag.Add("Key2", 200.10M); bag.Add("Key3", 300.10M); string xml = bag.ToXml(); TestContext.WriteLine(bag.ToXml()); bag.Clear(); bag.FromXml(xml); Assert.IsTrue(bag.Get("Key1") == 100.10M); Assert.IsTrue(bag.Get("Key3") == 300.10M); } and produces typed results of type decimal. The types can be either value or reference types the combination of which actually proved to be a little more tricky than anticipated due to null and specific string value checks required - getting the generic typing right required use of default(T) and Convert.ChangeType() to trick the compiler into playing nice. Of course the whole raison d'etre for this class is the XML serialization. You can see in the code above that we're doing a .ToXml() and .FromXml() to serialize to and from string. The XML produced for the first example looks like this: <?xml version="1.0" encoding="utf-8"?> <properties> <item> <key>key</key> <value>Value</value> </item> <item> <key>Key2</key> <value type="decimal">100.10</value> </item> <item> <key>Key3</key> <value type="___System.Guid"> <guid>f7a92032-0c6d-4e9d-9950-b15ff7cd207d</guid> </value> </item> <item> <key>Key4</key> <value type="datetime">2011-09-26T17:45:58.5789578-10:00</value> </item> <item> <key>Key5</key> <value type="boolean">true</value> </item> <item> <key>Key7</key> <value type="base64Binary">Ki1C</value> </item> <item> <key>Key8</key> <value type="nil" /> </item> <item> <key>Key9</key> <value type="___Westwind.Tools.Tests.PropertyBagTest+ComplexObject"> <ComplexObject> <Name>Rick</Name> <Entered>2011-09-26T17:45:58.5789578-10:00</Entered> <Count>10</Count> </ComplexObject> </value> </item> </properties>   The format is a bit cleaner than the DataContractSerializer. Each item is serialized into <key> <value> pairs. If the value is a string no type information is written. Since string tends to be the most common type this saves space and serialization processing. All other types are attributed. Simple types are mapped to XML types so things like decimal, datetime, boolean and base64Binary are encoded using their Xml type values. All other types are embedded with a hokey format that describes the .NET type preceded by a three underscores and then are encoded using the XmlSerializer. You can see this best above in the ComplexObject encoding. For custom types this isn't pretty either, but it's more concise than the DCS and it works as long as you're serializing back and forth between .NET clients at least. The XML generated from the second example that uses PropertyBag<decimal> looks like this: <?xml version="1.0" encoding="utf-8"?> <properties> <item> <key>key</key> <value type="decimal">10</value> </item> <item> <key>Key1</key> <value type="decimal">100.10</value> </item> <item> <key>Key2</key> <value type="decimal">200.10</value> </item> <item> <key>Key3</key> <value type="decimal">300.10</value> </item> </properties>   How does it work As I mentioned there's nothing fancy about this solution - it's little more than a subclass of Dictionary<T,V> that implements custom Xml Serialization and a couple of helper methods that facilitate getting the XML in and out of the class more easily. But it's proven very handy for a number of projects for me where dynamic data storage is required. Here's the code: /// <summary> /// Creates a serializable string/object dictionary that is XML serializable /// Encodes keys as element names and values as simple values with a type /// attribute that contains an XML type name. Complex names encode the type /// name with type='___namespace.classname' format followed by a standard xml /// serialized format. The latter serialization can be slow so it's not recommended /// to pass complex types if performance is critical. /// </summary> [XmlRoot("properties")] public class PropertyBag : PropertyBag<object> { /// <summary> /// Creates an instance of a propertybag from an Xml string /// </summary> /// <param name="xml">Serialize</param> /// <returns></returns> public static PropertyBag CreateFromXml(string xml) { var bag = new PropertyBag(); bag.FromXml(xml); return bag; } } /// <summary> /// Creates a serializable string for generic types that is XML serializable. /// /// Encodes keys as element names and values as simple values with a type /// attribute that contains an XML type name. Complex names encode the type /// name with type='___namespace.classname' format followed by a standard xml /// serialized format. The latter serialization can be slow so it's not recommended /// to pass complex types if performance is critical. /// </summary> /// <typeparam name="TValue">Must be a reference type. For value types use type object</typeparam> [XmlRoot("properties")] public class PropertyBag<TValue> : Dictionary<string, TValue>, IXmlSerializable { /// <summary> /// Not implemented - this means no schema information is passed /// so this won't work with ASMX/WCF services. /// </summary> /// <returns></returns> public System.Xml.Schema.XmlSchema GetSchema() { return null; } /// <summary> /// Serializes the dictionary to XML. Keys are /// serialized to element names and values as /// element values. An xml type attribute is embedded /// for each serialized element - a .NET type /// element is embedded for each complex type and /// prefixed with three underscores. /// </summary> /// <param name="writer"></param> public void WriteXml(System.Xml.XmlWriter writer) { foreach (string key in this.Keys) { TValue value = this[key]; Type type = null; if (value != null) type = value.GetType(); writer.WriteStartElement("item"); writer.WriteStartElement("key"); writer.WriteString(key as string); writer.WriteEndElement(); writer.WriteStartElement("value"); string xmlType = XmlUtils.MapTypeToXmlType(type); bool isCustom = false; // Type information attribute if not string if (value == null) { writer.WriteAttributeString("type", "nil"); } else if (!string.IsNullOrEmpty(xmlType)) { if (xmlType != "string") { writer.WriteStartAttribute("type"); writer.WriteString(xmlType); writer.WriteEndAttribute(); } } else { isCustom = true; xmlType = "___" + value.GetType().FullName; writer.WriteStartAttribute("type"); writer.WriteString(xmlType); writer.WriteEndAttribute(); } // Actual deserialization if (!isCustom) { if (value != null) writer.WriteValue(value); } else { XmlSerializer ser = new XmlSerializer(value.GetType()); ser.Serialize(writer, value); } writer.WriteEndElement(); // value writer.WriteEndElement(); // item } } /// <summary> /// Reads the custom serialized format /// </summary> /// <param name="reader"></param> public void ReadXml(System.Xml.XmlReader reader) { this.Clear(); while (reader.Read()) { if (reader.NodeType == XmlNodeType.Element && reader.Name == "key") { string xmlType = null; string name = reader.ReadElementContentAsString(); // item element reader.ReadToNextSibling("value"); if (reader.MoveToNextAttribute()) xmlType = reader.Value; reader.MoveToContent(); TValue value; if (xmlType == "nil") value = default(TValue); // null else if (string.IsNullOrEmpty(xmlType)) { // value is a string or object and we can assign TValue to value string strval = reader.ReadElementContentAsString(); value = (TValue) Convert.ChangeType(strval, typeof(TValue)); } else if (xmlType.StartsWith("___")) { while (reader.Read() && reader.NodeType != XmlNodeType.Element) { } Type type = ReflectionUtils.GetTypeFromName(xmlType.Substring(3)); //value = reader.ReadElementContentAs(type,null); XmlSerializer ser = new XmlSerializer(type); value = (TValue)ser.Deserialize(reader); } else value = (TValue)reader.ReadElementContentAs(XmlUtils.MapXmlTypeToType(xmlType), null); this.Add(name, value); } } } /// <summary> /// Serializes this dictionary to an XML string /// </summary> /// <returns>XML String or Null if it fails</returns> public string ToXml() { string xml = null; SerializationUtils.SerializeObject(this, out xml); return xml; } /// <summary> /// Deserializes from an XML string /// </summary> /// <param name="xml"></param> /// <returns>true or false</returns> public bool FromXml(string xml) { this.Clear(); // if xml string is empty we return an empty dictionary if (string.IsNullOrEmpty(xml)) return true; var result = SerializationUtils.DeSerializeObject(xml, this.GetType()) as PropertyBag<TValue>; if (result != null) { foreach (var item in result) { this.Add(item.Key, item.Value); } } else // null is a failure return false; return true; } /// <summary> /// Creates an instance of a propertybag from an Xml string /// </summary> /// <param name="xml"></param> /// <returns></returns> public static PropertyBag<TValue> CreateFromXml(string xml) { var bag = new PropertyBag<TValue>(); bag.FromXml(xml); return bag; } } } The code uses a couple of small helper classes SerializationUtils and XmlUtils for mapping Xml types to and from .NET, both of which are from the WestWind,Utilities project (which is the same project where PropertyBag lives) from the West Wind Web Toolkit. The code implements ReadXml and WriteXml for the IXmlSerializable implementation using old school XmlReaders and XmlWriters (because it's pretty simple stuff - no need for XLinq here). Then there are two helper methods .ToXml() and .FromXml() that basically allow your code to easily convert between XML and a PropertyBag object. In my code that's what I use to actually to persist to and from the entity XML property during .Load() and .Save() operations. It's sweet to be able to have a string key dictionary and then be able to turn around with 1 line of code to persist the whole thing to XML and back. Hopefully some of you will find this class as useful as I've found it. It's a simple solution to a common requirement in my applications and I've used the hell out of it in the  short time since I created it. Resources You can find the complete code for the two classes plus the helpers in the Subversion repository for Westwind.Utilities. You can grab the source files from there or download the whole project. You can also grab the full Westwind.Utilities assembly from NuGet and add it to your project if that's easier for you. PropertyBag Source Code SerializationUtils and XmlUtils Westwind.Utilities Assembly on NuGet (add from Visual Studio) © Rick Strahl, West Wind Technologies, 2005-2011Posted in .NET  CSharp   Tweet (function() { var po = document.createElement('script'); po.type = 'text/javascript'; po.async = true; po.src = 'https://apis.google.com/js/plusone.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(po, s); })();

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• Anyone know how to use TValue.AsType<TNotifyEvent> properly?

  - by Mason Wheeler

  I'm trying to use RTTI to add an event handler to a control, that may already have an event handler set. The code looks something like this: var prop: TRttiProperty; val: TValue; begin prop := FContext.GetType(MyControl.ClassInfo).GetProperty('OnChange'); val := prop.GetValue(MyControl); FOldOnChange := val.AsType<TNotifyEvent>; prop.SetValue(MyControl, TValue.From<TNotifyEvent>(self.MyOnChange)); end; I want this so I can do this in MyOnChange: begin if assigned(FOldOnChange) then FOldOnChange(Sender); //additional code here end; Unfortunately, the compiler doesn't seem to like the line FOldOnChange := val.AsType<TNotifyEvent>;. It says E2010 Incompatible types: 'procedure, untyped pointer or untyped parameter' and 'TNotifyEvent' Anyone know why that is or how to fix it? It looks right to me...

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• How can I make this work with deep properties

  - by Martin Robins

  Given the following code... class Program { static void Main(string[] args) { Foo foo = new Foo { Bar = new Bar { Name = "Martin" }, Name = "Martin" }; DoLambdaStuff(foo, f => f.Name); DoLambdaStuff(foo, f => f.Bar.Name); } static void DoLambdaStuff<TObject, TValue>(TObject obj, Expression<Func<TObject, TValue>> expression) { // Set up and test "getter"... Func<TObject, TValue> getValue = expression.Compile(); TValue stuff = getValue(obj); // Set up and test "setter"... ParameterExpression objectParameterExpression = Expression.Parameter(typeof(TObject)), valueParameterExpression = Expression.Parameter(typeof(TValue)); Expression<Action<TObject, TValue>> setValueExpression = Expression.Lambda<Action<TObject, TValue>>( Expression.Block( Expression.Assign(Expression.Property(objectParameterExpression, ((MemberExpression)expression.Body).Member.Name), valueParameterExpression) ), objectParameterExpression, valueParameterExpression ); Action<TObject, TValue> setValue = setValueExpression.Compile(); setValue(obj, stuff); } } class Foo { public Bar Bar { get; set; } public string Name { get; set; } } class Bar { public string Name { get; set; } } The call to DoLambdaStuff(foo, f => f.Name) works ok because I am accessing a shallow property, however the call to DoLambdaStuff(foo, f => f.Bar.Name) fails - although the creation of the getValue function works fine, the creation of the setValueExpression fails because I am attempting to access a deep property of the object. Can anybody please help me to modify this so that I can create the setValueExpression for deep properties as well as shallow? Thanks.

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• C#/.NET Fundamentals: Choosing the Right Collection Class

  - by James Michael Hare

  The .NET Base Class Library (BCL) has a wide array of collection classes at your disposal which make it easy to manage collections of objects. While it's great to have so many classes available, it can be daunting to choose the right collection to use for any given situation. As hard as it may be, choosing the right collection can be absolutely key to the performance and maintainability of your application! This post will look at breaking down any confusion between each collection and the situations in which they excel. We will be spending most of our time looking at the System.Collections.Generic namespace, which is the recommended set of collections. The Generic Collections: System.Collections.Generic namespace The generic collections were introduced in .NET 2.0 in the System.Collections.Generic namespace. This is the main body of collections you should tend to focus on first, as they will tend to suit 99% of your needs right up front. It is important to note that the generic collections are unsynchronized. This decision was made for performance reasons because depending on how you are using the collections its completely possible that synchronization may not be required or may be needed on a higher level than simple method-level synchronization. Furthermore, concurrent read access (all writes done at beginning and never again) is always safe, but for concurrent mixed access you should either synchronize the collection or use one of the concurrent collections. So let's look at each of the collections in turn and its various pros and cons, at the end we'll summarize with a table to help make it easier to compare and contrast the different collections. The Associative Collection Classes Associative collections store a value in the collection by providing a key that is used to add/remove/lookup the item. Hence, the container associates the value with the key. These collections are most useful when you need to lookup/manipulate a collection using a key value. For example, if you wanted to look up an order in a collection of orders by an order id, you might have an associative collection where they key is the order id and the value is the order. The Dictionary<TKey,TVale> is probably the most used associative container class. The Dictionary<TKey,TValue> is the fastest class for associative lookups/inserts/deletes because it uses a hash table under the covers. Because the keys are hashed, the key type should correctly implement GetHashCode() and Equals() appropriately or you should provide an external IEqualityComparer to the dictionary on construction. The insert/delete/lookup time of items in the dictionary is amortized constant time - O(1) - which means no matter how big the dictionary gets, the time it takes to find something remains relatively constant. This is highly desirable for high-speed lookups. The only downside is that the dictionary, by nature of using a hash table, is unordered, so you cannot easily traverse the items in a Dictionary in order. The SortedDictionary<TKey,TValue> is similar to the Dictionary<TKey,TValue> in usage but very different in implementation. The SortedDictionary<TKey,TValye> uses a binary tree under the covers to maintain the items in order by the key. As a consequence of sorting, the type used for the key must correctly implement IComparable<TKey> so that the keys can be correctly sorted. The sorted dictionary trades a little bit of lookup time for the ability to maintain the items in order, thus insert/delete/lookup times in a sorted dictionary are logarithmic - O(log n). Generally speaking, with logarithmic time, you can double the size of the collection and it only has to perform one extra comparison to find the item. Use the SortedDictionary<TKey,TValue> when you want fast lookups but also want to be able to maintain the collection in order by the key. The SortedList<TKey,TValue> is the other ordered associative container class in the generic containers. Once again SortedList<TKey,TValue>, like SortedDictionary<TKey,TValue>, uses a key to sort key-value pairs. Unlike SortedDictionary, however, items in a SortedList are stored as an ordered array of items. This means that insertions and deletions are linear - O(n) - because deleting or adding an item may involve shifting all items up or down in the list. Lookup time, however is O(log n) because the SortedList can use a binary search to find any item in the list by its key. So why would you ever want to do this? Well, the answer is that if you are going to load the SortedList up-front, the insertions will be slower, but because array indexing is faster than following object links, lookups are marginally faster than a SortedDictionary. Once again I'd use this in situations where you want fast lookups and want to maintain the collection in order by the key, and where insertions and deletions are rare. The Non-Associative Containers The other container classes are non-associative. They don't use keys to manipulate the collection but rely on the object itself being stored or some other means (such as index) to manipulate the collection. The List<T> is a basic contiguous storage container. Some people may call this a vector or dynamic array. Essentially it is an array of items that grow once its current capacity is exceeded. Because the items are stored contiguously as an array, you can access items in the List<T> by index very quickly. However inserting and removing in the beginning or middle of the List<T> are very costly because you must shift all the items up or down as you delete or insert respectively. However, adding and removing at the end of a List<T> is an amortized constant operation - O(1). Typically List<T> is the standard go-to collection when you don't have any other constraints, and typically we favor a List<T> even over arrays unless we are sure the size will remain absolutely fixed. The LinkedList<T> is a basic implementation of a doubly-linked list. This means that you can add or remove items in the middle of a linked list very quickly (because there's no items to move up or down in contiguous memory), but you also lose the ability to index items by position quickly. Most of the time we tend to favor List<T> over LinkedList<T> unless you are doing a lot of adding and removing from the collection, in which case a LinkedList<T> may make more sense. The HashSet<T> is an unordered collection of unique items. This means that the collection cannot have duplicates and no order is maintained. Logically, this is very similar to having a Dictionary<TKey,TValue> where the TKey and TValue both refer to the same object. This collection is very useful for maintaining a collection of items you wish to check membership against. For example, if you receive an order for a given vendor code, you may want to check to make sure the vendor code belongs to the set of vendor codes you handle. In these cases a HashSet<T> is useful for super-quick lookups where order is not important. Once again, like in Dictionary, the type T should have a valid implementation of GetHashCode() and Equals(), or you should provide an appropriate IEqualityComparer<T> to the HashSet<T> on construction. The SortedSet<T> is to HashSet<T> what the SortedDictionary<TKey,TValue> is to Dictionary<TKey,TValue>. That is, the SortedSet<T> is a binary tree where the key and value are the same object. This once again means that adding/removing/lookups are logarithmic - O(log n) - but you gain the ability to iterate over the items in order. For this collection to be effective, type T must implement IComparable<T> or you need to supply an external IComparer<T>. Finally, the Stack<T> and Queue<T> are two very specific collections that allow you to handle a sequential collection of objects in very specific ways. The Stack<T> is a last-in-first-out (LIFO) container where items are added and removed from the top of the stack. Typically this is useful in situations where you want to stack actions and then be able to undo those actions in reverse order as needed. The Queue<T> on the other hand is a first-in-first-out container which adds items at the end of the queue and removes items from the front. This is useful for situations where you need to process items in the order in which they came, such as a print spooler or waiting lines. So that's the basic collections. Let's summarize what we've learned in a quick reference table.  Collection Ordered? Contiguous Storage? Direct Access? Lookup Efficiency Manipulate Efficiency Notes Dictionary No Yes Via Key Key: O(1) O(1) Best for high performance lookups. SortedDictionary Yes No Via Key Key: O(log n) O(log n) Compromise of Dictionary speed and ordering, uses binary search tree. SortedList Yes Yes Via Key Key: O(log n) O(n) Very similar to SortedDictionary, except tree is implemented in an array, so has faster lookup on preloaded data, but slower loads. List No Yes Via Index Index: O(1) Value: O(n) O(n) Best for smaller lists where direct access required and no ordering. LinkedList No No No Value: O(n) O(1) Best for lists where inserting/deleting in middle is common and no direct access required. HashSet No Yes Via Key Key: O(1) O(1) Unique unordered collection, like a Dictionary except key and value are same object. SortedSet Yes No Via Key Key: O(log n) O(log n) Unique ordered collection, like SortedDictionary except key and value are same object. Stack No Yes Only Top Top: O(1) O(1)* Essentially same as List<T> except only process as LIFO Queue No Yes Only Front Front: O(1) O(1) Essentially same as List<T> except only process as FIFO   The Original Collections: System.Collections namespace The original collection classes are largely considered deprecated by developers and by Microsoft itself. In fact they indicate that for the most part you should always favor the generic or concurrent collections, and only use the original collections when you are dealing with legacy .NET code. Because these collections are out of vogue, let's just briefly mention the original collection and their generic equivalents: ArrayList A dynamic, contiguous collection of objects. Favor the generic collection List<T> instead. Hashtable Associative, unordered collection of key-value pairs of objects. Favor the generic collection Dictionary<TKey,TValue> instead. Queue First-in-first-out (FIFO) collection of objects. Favor the generic collection Queue<T> instead. SortedList Associative, ordered collection of key-value pairs of objects. Favor the generic collection SortedList<T> instead. Stack Last-in-first-out (LIFO) collection of objects. Favor the generic collection Stack<T> instead. In general, the older collections are non-type-safe and in some cases less performant than their generic counterparts. Once again, the only reason you should fall back on these older collections is for backward compatibility with legacy code and libraries only. The Concurrent Collections: System.Collections.Concurrent namespace The concurrent collections are new as of .NET 4.0 and are included in the System.Collections.Concurrent namespace. These collections are optimized for use in situations where multi-threaded read and write access of a collection is desired. The concurrent queue, stack, and dictionary work much as you'd expect. The bag and blocking collection are more unique. Below is the summary of each with a link to a blog post I did on each of them. ConcurrentQueue Thread-safe version of a queue (FIFO). For more information see: C#/.NET Little Wonders: The ConcurrentStack and ConcurrentQueue ConcurrentStack Thread-safe version of a stack (LIFO). For more information see: C#/.NET Little Wonders: The ConcurrentStack and ConcurrentQueue ConcurrentBag Thread-safe unordered collection of objects. Optimized for situations where a thread may be bother reader and writer. For more information see: C#/.NET Little Wonders: The ConcurrentBag and BlockingCollection ConcurrentDictionary Thread-safe version of a dictionary. Optimized for multiple readers (allows multiple readers under same lock). For more information see C#/.NET Little Wonders: The ConcurrentDictionary BlockingCollection Wrapper collection that implement producers & consumers paradigm. Readers can block until items are available to read. Writers can block until space is available to write (if bounded). For more information see C#/.NET Little Wonders: The ConcurrentBag and BlockingCollection Summary The .NET BCL has lots of collections built in to help you store and manipulate collections of data. Understanding how these collections work and knowing in which situations each container is best is one of the key skills necessary to build more performant code. Choosing the wrong collection for the job can make your code much slower or even harder to maintain if you choose one that doesn’t perform as well or otherwise doesn’t exactly fit the situation. Remember to avoid the original collections and stick with the generic collections.  If you need concurrent access, you can use the generic collections if the data is read-only, or consider the concurrent collections for mixed-access if you are running on .NET 4.0 or higher.   Tweet Technorati Tags: C#,.NET,Collecitons,Generic,Concurrent,Dictionary,List,Stack,Queue,SortedList,SortedDictionary,HashSet,SortedSet

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• Merging dictionaries in C#

  - by orip

  What's the best way to merge 2 or more dictionaries (Dictionary<T1,T2>) in C#? (3.0 features like LINQ are fine). I'm thinking of a method signature along the lines of: public static Dictionary<TKey,TValue> Merge<TKey,TValue>(Dictionary<TKey,TValue>[] dictionaries); or public static Dictionary<TKey,TValue> Merge<TKey,TValue>(IEnumerable<Dictionary<TKey,TValue>> dictionaries); EDIT: Got a cool solution from JaredPar and Jon Skeet, but I was thinking of something that handles duplicate keys. In case of collision, it doesn't matter which value is saved to the dict as long as it's consistent.

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• using dictionaries with WebServices

  - by umit-alba

  Hi! I tried to pass a dictionary via WebServices. However it is not serializeable. So i wrote an Own Class that makes it serializeable: using System; using System.Net; using System.Windows; using System.Collections.Generic; using System.Xml.Serialization; using System.Xml; using System.Xml.Schema; namespace Platform { public class SaDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IXmlSerializable { #region Constructors public SaDictionary() : base() { } public SaDictionary(IDictionary<TKey, TValue> dictionary) : base(dictionary) { } public SaDictionary(IEqualityComparer<TKey> comparer) : base(comparer) { } public SaDictionary(int capacity) : base(capacity) { } public SaDictionary(IDictionary<TKey, TValue> dictionary, IEqualityComparer<TKey> comparer) : base(dictionary, comparer) { } public SaDictionary(int capacity, IEqualityComparer<TKey> comparer) : base(capacity, comparer) { } //protected SaDictionary(SerializationInfo info, StreamingContext context) // : base(info, context) //{ //} #endregion public XmlSchema GetSchema() { return null; } public void ReadXml(XmlReader reader) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); bool wasEmpty = reader.IsEmptyElement; reader.Read(); if (wasEmpty) return; while (reader.NodeType != XmlNodeType.EndElement) { reader.ReadStartElement("item"); reader.ReadStartElement("key"); TKey key = (TKey)keySerializer.Deserialize(reader); reader.ReadEndElement(); //key reader.ReadStartElement("value"); TValue value = (TValue)valueSerializer.Deserialize(reader); reader.ReadEndElement(); //value this.Add(key, value); reader.ReadEndElement(); //item // reader.MoveToContent(); } reader.ReadEndElement(); } public void WriteXml(XmlWriter writer) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); foreach (TKey key in this.Keys) { writer.WriteStartElement("item"); writer.WriteStartElement("key"); keySerializer.Serialize(writer, key); writer.WriteEndElement(); //key writer.WriteStartElement("value"); TValue value = this[key]; valueSerializer.Serialize(writer, value); writer.WriteEndElement(); //value writer.WriteEndElement(); //item } } } } However i get an ArrayOfXElement back. Is there a way to cast it back to a Dictionary? greets

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• How I understood monads, part 1/2: sleepless and self-loathing in Seattle

  - by Bertrand Le Roy

  For some time now, I had been noticing some interest for monads, mostly in the form of unintelligible (to me) blog posts and comments saying “oh, yeah, that’s a monad” about random stuff as if it were absolutely obvious and if I didn’t know what they were talking about, I was probably an uneducated idiot, ignorant about the simplest and most fundamental concepts of functional programming. Fair enough, I am pretty much exactly that. Being the kind of guy who can spend eight years in college just to understand a few interesting concepts about the universe, I had to check it out and try to understand monads so that I too can say “oh, yeah, that’s a monad”. Man, was I hit hard in the face with the limitations of my own abstract thinking abilities. All the articles I could find about the subject seemed to be vaguely understandable at first but very quickly overloaded the very few concept slots I have available in my brain. They also seemed to be consistently using arcane notation that I was entirely unfamiliar with. It finally all clicked together one Friday afternoon during the team’s beer symposium when Louis was patient enough to break it down for me in a language I could understand (C#). I don’t know if being intoxicated helped. Feel free to read this with or without a drink in hand. So here it is in a nutshell: a monad allows you to manipulate stuff in interesting ways. Oh, OK, you might say. Yeah. Exactly. Let’s start with a trivial case: public static class Trivial { public static TResult Execute<T, TResult>( this T argument, Func<T, TResult> operation) { return operation(argument); } } This is not a monad. I removed most concepts here to start with something very simple. There is only one concept here: the idea of executing an operation on an object. This is of course trivial and it would actually be simpler to just apply that operation directly on the object. But please bear with me, this is our first baby step. Here’s how you use that thing: "some string" .Execute(s => s + " processed by trivial proto-monad.") .Execute(s => s + " And it's chainable!"); What we’re doing here is analogous to having an assembly chain in a factory: you can feed it raw material (the string here) and a number of machines that each implement a step in the manufacturing process and you can start building stuff. The Trivial class here represents the empty assembly chain, the conveyor belt if you will, but it doesn’t care what kind of raw material gets in, what gets out or what each machine is doing. It is pure process. A real monad will need a couple of additional concepts. Let’s say the conveyor belt needs the material to be processed to be contained in standardized boxes, just so that it can safely and efficiently be transported from machine to machine or so that tracking information can be attached to it. Each machine knows how to treat raw material or partly processed material, but it doesn’t know how to treat the boxes so the conveyor belt will have to extract the material from the box before feeding it into each machine, and it will have to box it back afterwards. This conveyor belt with boxes is essentially what a monad is. It has one method to box stuff, one to extract stuff from its box and one to feed stuff into a machine. So let’s reformulate the previous example but this time with the boxes, which will do nothing for the moment except containing stuff. public class Identity<T> { public Identity(T value) { Value = value; } public T Value { get; private set;} public static Identity<T> Unit(T value) { return new Identity<T>(value); } public static Identity<U> Bind<U>( Identity<T> argument, Func<T, Identity<U>> operation) { return operation(argument.Value); } } Now this is a true to the definition Monad, including the weird naming of the methods. It is the simplest monad, called the identity monad and of course it does nothing useful. Here’s how you use it: Identity<string>.Bind( Identity<string>.Unit("some string"), s => Identity<string>.Unit( s + " was processed by identity monad.")).Value That of course is seriously ugly. Note that the operation is responsible for re-boxing its result. That is a part of strict monads that I don’t quite get and I’ll take the liberty to lift that strange constraint in the next examples. To make this more readable and easier to use, let’s build a few extension methods: public static class IdentityExtensions { public static Identity<T> ToIdentity<T>(this T value) { return new Identity<T>(value); } public static Identity<U> Bind<T, U>( this Identity<T> argument, Func<T, U> operation) { return operation(argument.Value).ToIdentity(); } } With those, we can rewrite our code as follows: "some string".ToIdentity() .Bind(s => s + " was processed by monad extensions.") .Bind(s => s + " And it's chainable...") .Value; This is considerably simpler but still retains the qualities of a monad. But it is still pointless. Let’s look at a more useful example, the state monad, which is basically a monad where the boxes have a label. It’s useful to perform operations on arbitrary objects that have been enriched with an attached state object. public class Stateful<TValue, TState> { public Stateful(TValue value, TState state) { Value = value; State = state; } public TValue Value { get; private set; } public TState State { get; set; } } public static class StateExtensions { public static Stateful<TValue, TState> ToStateful<TValue, TState>( this TValue value, TState state) { return new Stateful<TValue, TState>(value, state); } public static Stateful<TResult, TState> Execute<TValue, TState, TResult>( this Stateful<TValue, TState> argument, Func<TValue, TResult> operation) { return operation(argument.Value) .ToStateful(argument.State); } } You can get a stateful version of any object by calling the ToStateful extension method, passing the state object in. You can then execute ordinary operations on the values while retaining the state: var statefulInt = 3.ToStateful("This is the state"); var processedStatefulInt = statefulInt .Execute(i => ++i) .Execute(i => i * 10) .Execute(i => i + 2); Console.WriteLine("Value: {0}; state: {1}", processedStatefulInt.Value, processedStatefulInt.State); This monad differs from the identity by enriching the boxes. There is another way to give value to the monad, which is to enrich the processing. An example of that is the writer monad, which can be typically used to log the operations that are being performed by the monad. Of course, the richest monads enrich both the boxes and the processing. That’s all for today. I hope with this you won’t have to go through the same process that I did to understand monads and that you haven’t gone into concept overload like I did. Next time, we’ll examine some examples that you already know but we will shine the monadic light, hopefully illuminating them in a whole new way. Realizing that this pattern is actually in many places but mostly unnoticed is what will enable the truly casual “oh, yes, that’s a monad” comments. Here’s the code for this article: http://weblogs.asp.net/blogs/bleroy/Samples/Monads.zip The Wikipedia article on monads: http://en.wikipedia.org/wiki/Monads_in_functional_programming This article was invaluable for me in understanding how to express the canonical monads in C# (interesting Linq stuff in there): http://blogs.msdn.com/b/wesdyer/archive/2008/01/11/the-marvels-of-monads.aspx

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• Control XML serialization of Dictionary<K, T>

  - by Luca

  I'm investigating about XML serialization, and since I use lot of dictionary, I would like to serialize them as well. I found the following solution for that (I'm quite proud of it! :) ). [XmlInclude(typeof(Foo))] public class XmlDictionary<TKey, TValue> { /// <summary> /// Key/value pair. /// </summary> public struct DictionaryItem { /// <summary> /// Dictionary item key. /// </summary> public TKey Key; /// <summary> /// Dictionary item value. /// </summary> public TValue Value; } /// <summary> /// Dictionary items. /// </summary> public DictionaryItem[] Items { get { List<DictionaryItem> items = new List<DictionaryItem>(ItemsDictionary.Count); foreach (KeyValuePair<TKey, TValue> pair in ItemsDictionary) { DictionaryItem item; item.Key = pair.Key; item.Value = pair.Value; items.Add(item); } return (items.ToArray()); } set { ItemsDictionary = new Dictionary<TKey,TValue>(); foreach (DictionaryItem item in value) ItemsDictionary.Add(item.Key, item.Value); } } /// <summary> /// Indexer base on dictionary key. /// </summary> /// <param name="key"></param> /// <returns></returns> public TValue this[TKey key] { get { return (ItemsDictionary[key]); } set { Debug.Assert(value != null); ItemsDictionary[key] = value; } } /// <summary> /// Delegate for get key from a dictionary value. /// </summary> /// <param name="value"></param> /// <returns></returns> public delegate TKey GetItemKeyDelegate(TValue value); /// <summary> /// Add a range of values automatically determining the associated keys. /// </summary> /// <param name="values"></param> /// <param name="keygen"></param> public void AddRange(IEnumerable<TValue> values, GetItemKeyDelegate keygen) { foreach (TValue v in values) ItemsDictionary.Add(keygen(v), v); } /// <summary> /// Items dictionary. /// </summary> [XmlIgnore] public Dictionary<TKey, TValue> ItemsDictionary = new Dictionary<TKey,TValue>(); } The classes deriving from this class are serialized in the following way: <FooDictionary xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Items> <DictionaryItemOfInt32Foo> <Key/> <Value/> </DictionaryItemOfInt32XmlProcess> <Items> This give me a good solution, but: How can I control the name of the element DictionaryItemOfInt32Foo What happens if I define a Dictionary<FooInt32, Int32> and I have the classes Foo and FooInt32? Is it possible to optimize the class above? THank you very much!

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• Control XML serialization of generic types

  - by Luca

  I'm investigating about XML serialization, and since I use lot of dictionary, I would like to serialize them as well. I found the following solution for that (I'm quite proud of it! :) ). [XmlInclude(typeof(Foo))] public class XmlDictionary<TKey, TValue> { /// <summary> /// Key/value pair. /// </summary> public struct DictionaryItem { /// <summary> /// Dictionary item key. /// </summary> public TKey Key; /// <summary> /// Dictionary item value. /// </summary> public TValue Value; } /// <summary> /// Dictionary items. /// </summary> public DictionaryItem[] Items { get { List<DictionaryItem> items = new List<DictionaryItem>(ItemsDictionary.Count); foreach (KeyValuePair<TKey, TValue> pair in ItemsDictionary) { DictionaryItem item; item.Key = pair.Key; item.Value = pair.Value; items.Add(item); } return (items.ToArray()); } set { ItemsDictionary = new Dictionary<TKey,TValue>(); foreach (DictionaryItem item in value) ItemsDictionary.Add(item.Key, item.Value); } } /// <summary> /// Indexer base on dictionary key. /// </summary> /// <param name="key"></param> /// <returns></returns> public TValue this[TKey key] { get { return (ItemsDictionary[key]); } set { Debug.Assert(value != null); ItemsDictionary[key] = value; } } /// <summary> /// Delegate for get key from a dictionary value. /// </summary> /// <param name="value"></param> /// <returns></returns> public delegate TKey GetItemKeyDelegate(TValue value); /// <summary> /// Add a range of values automatically determining the associated keys. /// </summary> /// <param name="values"></param> /// <param name="keygen"></param> public void AddRange(IEnumerable<TValue> values, GetItemKeyDelegate keygen) { foreach (TValue v in values) ItemsDictionary.Add(keygen(v), v); } /// <summary> /// Items dictionary. /// </summary> [XmlIgnore] public Dictionary<TKey, TValue> ItemsDictionary = new Dictionary<TKey,TValue>(); } The classes deriving from this class are serialized in the following way: <XmlProcessList xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <Items> <DictionaryItemOfInt32Foo> <Key/> <Value/> </DictionaryItemOfInt32XmlProcess> <Items> This give me a good solution, but: How can I control the name of the element DictionaryItemOfInt32Foo What happens if I define a Dictionary<FooInt32, Int32> and I have the classes Foo and FooInt32? Is it possible to optimize the class above? THank you very much!

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• .NET XML serialization gotchas?

  - by kurious

  I've run into a few gotchas when doing C# XML serialization that I thought I'd share: You can't serialize items that are read-only (like KeyValuePairs) You can't serialize a generic dictionary. Instead, try this wrapper class (from http://weblogs.asp.net/pwelter34/archive/2006/05/03/444961.aspx): using System; using System.Collections.Generic; using System.Text; using System.Xml.Serialization; [XmlRoot("dictionary")] public class SerializableDictionary<TKey, TValue> : Dictionary<TKey, TValue>, IXmlSerializable { public System.Xml.Schema.XmlSchema GetSchema() { return null; } public void ReadXml(System.Xml.XmlReader reader) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); bool wasEmpty = reader.IsEmptyElement; reader.Read(); if (wasEmpty) return; while (reader.NodeType != System.Xml.XmlNodeType.EndElement) { reader.ReadStartElement("item"); reader.ReadStartElement("key"); TKey key = (TKey)keySerializer.Deserialize(reader); reader.ReadEndElement(); reader.ReadStartElement("value"); TValue value = (TValue)valueSerializer.Deserialize(reader); reader.ReadEndElement(); this.Add(key, value); reader.ReadEndElement(); reader.MoveToContent(); } reader.ReadEndElement(); } public void WriteXml(System.Xml.XmlWriter writer) { XmlSerializer keySerializer = new XmlSerializer(typeof(TKey)); XmlSerializer valueSerializer = new XmlSerializer(typeof(TValue)); foreach (TKey key in this.Keys) { writer.WriteStartElement("item"); writer.WriteStartElement("key"); keySerializer.Serialize(writer, key); writer.WriteEndElement(); writer.WriteStartElement("value"); TValue value = this[key]; valueSerializer.Serialize(writer, value); writer.WriteEndElement(); writer.WriteEndElement(); } } } Any other XML gotchas out there?

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• IXmlSerializable Dictionary

  - by Shimmy

  I was trying to create a generic Dictionary that implements IXmlSerializable. Here is my trial: Sub Main() Dim z As New SerializableDictionary(Of String, String) z.Add("asdf", "asd") Console.WriteLine(z.Serialize) End Sub Result: <?xml version="1.0" encoding="utf-16"?><Entry key="asdf" value="asd" /> I placed a breakpoint on top of the WriteXml method and I see that when it stops, the writer contains no data at all, and IMHO it should contain the root element and the xml declaration. <Serializable()> _ Public Class SerializableDictionary(Of TKey, TValue) : Inherits Dictionary(Of TKey, TValue) : Implements IXmlSerializable Private Const EntryString As String = "Entry" Private Const KeyString As String = "key" Private Const ValueString As String = "value" Private Shared ReadOnly AttributableTypes As Type() = New Type() {GetType(Boolean), GetType(Byte), GetType(Char), GetType(DateTime), GetType(Decimal), GetType(Double), GetType([Enum]), GetType(Guid), GetType(Int16), GetType(Int32), GetType(Int64), GetType(SByte), GetType(Single), GetType(String), GetType(TimeSpan), GetType(UInt16), GetType(UInt32), GetType(UInt64)} Private Shared ReadOnly GetIsAttributable As Predicate(Of Type) = Function(t) AttributableTypes.Contains(t) Private Shared ReadOnly IsKeyAttributable As Boolean = GetIsAttributable(GetType(TKey)) Private Shared ReadOnly IsValueAttributable As Boolean = GetIsAttributable(GetType(TValue)) Private Shared ReadOnly GetElementName As Func(Of Boolean, String) = Function(isKey) If(isKey, KeyString, ValueString) Public Function GetSchema() As System.Xml.Schema.XmlSchema Implements System.Xml.Serialization.IXmlSerializable.GetSchema Return Nothing End Function Public Sub WriteXml(ByVal writer As XmlWriter) Implements IXmlSerializable.WriteXml For Each entry In Me writer.WriteStartElement(EntryString) WriteData(IsKeyAttributable, writer, True, entry.Key) WriteData(IsValueAttributable, writer, False, entry.Value) writer.WriteEndElement() Next End Sub Private Sub WriteData(Of T)(ByVal attributable As Boolean, ByVal writer As XmlWriter, ByVal isKey As Boolean, ByVal value As T) Dim name = GetElementName(isKey) If attributable Then writer.WriteAttributeString(name, value.ToString) Else Dim serializer As New XmlSerializer(GetType(T)) writer.WriteStartElement(name) serializer.Serialize(writer, value) writer.WriteEndElement() End If End Sub Public Sub ReadXml(ByVal reader As XmlReader) Implements IXmlSerializable.ReadXml Dim empty = reader.IsEmptyElement reader.Read() If empty Then Exit Sub Clear() While reader.NodeType <> XmlNodeType.EndElement While reader.NodeType = XmlNodeType.Whitespace reader.Read() Dim key = ReadData(Of TKey)(IsKeyAttributable, reader, True) Dim value = ReadData(Of TValue)(IsValueAttributable, reader, False) Add(key, value) If Not IsKeyAttributable AndAlso Not IsValueAttributable Then reader.ReadEndElement() Else reader.Read() While reader.NodeType = XmlNodeType.Whitespace reader.Read() End While End While reader.ReadEndElement() End While End Sub Private Function ReadData(Of T)(ByVal attributable As Boolean, ByVal reader As XmlReader, ByVal isKey As Boolean) As T Dim name = GetElementName(isKey) Dim type = GetType(T) If attributable Then Return Convert.ChangeType(reader.GetAttribute(name), type) Else Dim serializer As New XmlSerializer(type) While reader.Name <> name reader.Read() End While reader.ReadStartElement(name) Dim value = serializer.Deserialize(reader) reader.ReadEndElement() Return value End If End Function Public Shared Function Serialize(ByVal dictionary As SerializableDictionary(Of TKey, TValue)) As String Dim sb As New StringBuilder(1024) Dim sw As New StringWriter(sb) Dim xs As New XmlSerializer(GetType(SerializableDictionary(Of TKey, TValue))) xs.Serialize(sw, dictionary) sw.Dispose() Return sb.ToString End Function Public Shared Function Deserialize(ByVal xml As String) As SerializableDictionary(Of TKey, TValue) Dim xs As New XmlSerializer(GetType(SerializableDictionary(Of TKey, TValue))) Dim xr As New XmlTextReader(xml, XmlNodeType.Document, Nothing) Return xs.Deserialize(xr) xr.Close() End Function Public Function Serialize() As String Dim sb As New StringBuilder Dim xw = XmlWriter.Create(sb) WriteXml(xw) xw.Close() Return sb.ToString End Function Public Sub Parse(ByVal xml As String) Dim xr As New XmlTextReader(xml, XmlNodeType.Document, Nothing) ReadXml(xr) xr.Close() End Sub End Class

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• IXmlSerializable Dictionary problem

  - by Shimmy

  I was trying to create a generic Dictionary that implements IXmlSerializable. Here is my trial: Sub Main() Dim z As New SerializableDictionary(Of String, String) z.Add("asdf", "asd") Console.WriteLine(z.Serialize) End Sub Result: <?xml version="1.0" encoding="utf-16"?><Entry key="asdf" value="asd" /> I placed a breakpoint on top of the WriteXml method and I see that when it stops, the writer contains no data at all, and IMHO it should contain the root element and the xml declaration. <Serializable()> _ Public Class SerializableDictionary(Of TKey, TValue) : Inherits Dictionary(Of TKey, TValue) : Implements IXmlSerializable Private Const EntryString As String = "Entry" Private Const KeyString As String = "key" Private Const ValueString As String = "value" Private Shared ReadOnly AttributableTypes As Type() = New Type() {GetType(Boolean), GetType(Byte), GetType(Char), GetType(DateTime), GetType(Decimal), GetType(Double), GetType([Enum]), GetType(Guid), GetType(Int16), GetType(Int32), GetType(Int64), GetType(SByte), GetType(Single), GetType(String), GetType(TimeSpan), GetType(UInt16), GetType(UInt32), GetType(UInt64)} Private Shared ReadOnly GetIsAttributable As Predicate(Of Type) = Function(t) AttributableTypes.Contains(t) Private Shared ReadOnly IsKeyAttributable As Boolean = GetIsAttributable(GetType(TKey)) Private Shared ReadOnly IsValueAttributable As Boolean = GetIsAttributable(GetType(TValue)) Private Shared ReadOnly GetElementName As Func(Of Boolean, String) = Function(isKey) If(isKey, KeyString, ValueString) Public Function GetSchema() As System.Xml.Schema.XmlSchema Implements System.Xml.Serialization.IXmlSerializable.GetSchema Return Nothing End Function Public Sub WriteXml(ByVal writer As XmlWriter) Implements IXmlSerializable.WriteXml For Each entry In Me writer.WriteStartElement(EntryString) WriteData(IsKeyAttributable, writer, True, entry.Key) WriteData(IsValueAttributable, writer, False, entry.Value) writer.WriteEndElement() Next End Sub Private Sub WriteData(Of T)(ByVal attributable As Boolean, ByVal writer As XmlWriter, ByVal isKey As Boolean, ByVal value As T) Dim name = GetElementName(isKey) If attributable Then writer.WriteAttributeString(name, value.ToString) Else Dim serializer As New XmlSerializer(GetType(T)) writer.WriteStartElement(name) serializer.Serialize(writer, value) writer.WriteEndElement() End If End Sub Public Sub ReadXml(ByVal reader As XmlReader) Implements IXmlSerializable.ReadXml Dim empty = reader.IsEmptyElement reader.Read() If empty Then Exit Sub Clear() While reader.NodeType <> XmlNodeType.EndElement While reader.NodeType = XmlNodeType.Whitespace reader.Read() Dim key = ReadData(Of TKey)(IsKeyAttributable, reader, True) Dim value = ReadData(Of TValue)(IsValueAttributable, reader, False) Add(key, value) If Not IsKeyAttributable AndAlso Not IsValueAttributable Then reader.ReadEndElement() Else reader.Read() While reader.NodeType = XmlNodeType.Whitespace reader.Read() End While End While reader.ReadEndElement() End While End Sub Private Function ReadData(Of T)(ByVal attributable As Boolean, ByVal reader As XmlReader, ByVal isKey As Boolean) As T Dim name = GetElementName(isKey) Dim type = GetType(T) If attributable Then Return Convert.ChangeType(reader.GetAttribute(name), type) Else Dim serializer As New XmlSerializer(type) While reader.Name <> name reader.Read() End While reader.ReadStartElement(name) Dim value = serializer.Deserialize(reader) reader.ReadEndElement() Return value End If End Function Public Shared Function Serialize(ByVal dictionary As SerializableDictionary(Of TKey, TValue)) As String Dim sb As New StringBuilder(1024) Dim sw As New StringWriter(sb) Dim xs As New XmlSerializer(GetType(SerializableDictionary(Of TKey, TValue))) xs.Serialize(sw, dictionary) sw.Dispose() Return sb.ToString End Function Public Shared Function Deserialize(ByVal xml As String) As SerializableDictionary(Of TKey, TValue) Dim xs As New XmlSerializer(GetType(SerializableDictionary(Of TKey, TValue))) Dim xr As New XmlTextReader(xml, XmlNodeType.Document, Nothing) Return xs.Deserialize(xr) xr.Close() End Function Public Function Serialize() As String Dim sb As New StringBuilder Dim xw = XmlWriter.Create(sb) WriteXml(xw) xw.Close() Return sb.ToString End Function Public Sub Parse(ByVal xml As String) Dim xr As New XmlTextReader(xml, XmlNodeType.Document, Nothing) ReadXml(xr) xr.Close() End Sub End Class

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• How do I write test code to exercise a C# generic Pair<TKey, TValue> ?

  - by Scott Davies

  Hi, I am reading through Jon Skeet's "C# in Depth", first edition (which is a great book). I'm in section 3.3.3, page 84, "Implementing Generics". Generics always confuse me, so I wrote some code to exercise the sample. The code provided is: using System; using System.Collections.Generic; public sealed class Pair<TFirst, TSecond> : IEquatable<Pair<TFirst, TSecond>> { private readonly TFirst first; private readonly TSecond second; public Pair(TFirst first, TSecond second) { this.first = first; this.second = second; } ...property getters... public bool Equals(Pair<TFirst, TSecond> other) { if (other == null) { return false; } return EqualityComparer<TFirst>.Default.Equals(this.First, other.First) && EqualityComparer<TSecond>.Default.Equals(this.Second, other.Second); } My code is: class MyClass { public static void Main (string[] args) { // Create new pair. Pair thePair = new Pair(new String("1"), new String("1")); // Compare a new pair to previous pair by generating a second pair. if (thePair.Equals(new Pair(new string("1"), new string("1")))) System.Console.WriteLine("Equal"); else System.Console.WriteLine("Not equal"); } } The compiler complains: "Using the generic type 'ManningListing36.Paie' requires 2 type argument(s) CS0305" What am I doing wrong ? Thanks, Scott

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• WPF Designer has bug with parsing generic control with overrided property

  - by Ivan Laktyunkin

  I've created a generic lookless control with virtual property: public abstract class TestControlBase<TValue> : Control { public static readonly DependencyProperty ValueProperty; static TestControlBase() { ValueProperty = DependencyProperty.Register("Value", typeof(TValue), typeof(TestControlBase<TValue>)); } protected TestControlBase() { Focusable = false; Value = default(TValue); } public virtual TValue Value { get { return (TValue)GetValue(ValueProperty); } set { SetValue(ValueProperty, value); } } } Then I've made a control derived from it and overrided Value property: public class TestControl : TestControlBase<int> { public override int Value { get { return base.Value; } set { base.Value = value; } } } So I use it in a Window XAML: <TestControls:TestControl /> When I open window in designer all is OK, but when I put mouse cursor to this line, or to this control in designer I receive exception: Exception has been thrown by the target of an invocation. at System.RuntimeMethodHandle._InvokeMethodFast(Object target, Object[] arguments, SignatureStruct& sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.RuntimeMethodHandle.InvokeMethodFast(Object target, Object[] arguments, Signature sig, MethodAttributes methodAttributes, RuntimeTypeHandle typeOwner) at System.Reflection.RuntimeMethodInfo.Invoke(Object obj, BindingFlags invokeAttr, Binder binder, Object[] parameters, CultureInfo culture, Boolean skipVisibilityChecks) at System.Delegate.DynamicInvokeImpl(Object[] args) at System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Boolean isSingleParameter) at System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Boolean isSingleParameter, Delegate catchHandler) Ambiguous match found. at System.RuntimeType.GetPropertyImpl(String name, BindingFlags bindingAttr, Binder binder, Type returnType, Type[] types, ParameterModifier[] modifiers) at System.Type.GetProperty(String name) at MS.Internal.ComponentModel.DependencyPropertyKind.get_IsDirect() at MS.Internal.ComponentModel.DependencyPropertyKind.get_IsAttached() at MS.Internal.ComponentModel.APCustomTypeDescriptor.GetProperties(Attribute[] attributes) at MS.Internal.ComponentModel.APCustomTypeDescriptor.GetProperties() at System.ComponentModel.TypeDescriptor.TypeDescriptionNode.DefaultExtendedTypeDescriptor.System.ComponentModel.ICustomTypeDescriptor.GetProperties() at System.ComponentModel.TypeDescriptor.GetPropertiesImpl(Object component, Attribute[] attributes, Boolean noCustomTypeDesc, Boolean noAttributes) at System.ComponentModel.TypeDescriptor.GetProperties(Object component) at MS.Internal.Model.ModelPropertyCollectionImpl.GetProperties(String propertyNameHint) at MS.Internal.Model.ModelPropertyCollectionImpl.<GetEnumerator>d__0.MoveNext() at MS.Internal.Designer.PropertyEditing.Model.ModelPropertyMerger.<GetFirstProperties>d__0.MoveNext() at MS.Internal.Designer.PropertyEditing.PropertyInspector.UpdateCategories(Selection selection) at MS.Internal.Designer.PropertyEditing.PropertyInspector.OnSelectionChangedIdle() Who know this problem? Please explain :) I have no ideas except that WPF Designer doesn't like generics. If I replace generics by Object all is OK.

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• LINQ query code for complex merging of data.

  - by Stacey

  I've posted this before, but I worded it poorly. I'm trying again with a more well thought out structure. Re-writing this a bit to make it more clear. I have the following code and I am trying to figure out the shorter linq expression to do it 'inline'. Please examine the "Run()" method near the bottom. I am attempting to understand how to join two dictionaries together based on a matching identifier in one of the objects - so that I can use the query in this sort of syntax. var selected = from a in items.List() // etc. etc. select a; This is my class structure. The Run() method is what I am trying to simplify. I basically need to do this conversion inline in a couple of places, and I wanted to simplify it a great deal so that I can define it more 'cleanly'. class TModel { public Guid Id { get; set; } } class TModels : List<TModel> { } class TValue { } class TStorage { public Dictionary<Guid, TValue> Items { get; set; } } class TArranged { public Dictionary<TModel, TValue> Items { get; set; } } static class Repository { static public TItem Single<TItem, TCollection>(Predicate<TItem> expression) { return default(TItem); // access logic. } } class Sample { public void Run() { TStorage tStorage = new TStorage(); // access tStorage logic here. Dictionary<TModel, TValue> d = new Dictionary<TModel, TValue>(); foreach (KeyValuePair<Guid, TValue> kv in tStorage.Items) { d.Add(Repository.Single<TModel, TModels>(m => m.Id == kv.Key),kv.Value); } } }

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• What should the name of this class be?

  - by Tim Murphy

  Naming classes is sometimes hard. What do you think name of the class should be? I originally created the class to use as a cache but can see its may have other uses. Example code to use the class. Dim cache = New NamePendingDictionary(Of String, Sample) Dim value = cache("a", Function() New Sample()) And here is the class that needs a name. ''' <summary> ''' Enhancement of <see cref="System.Collections.Generic.Dictionary"/>. See the Item property ''' for more details. ''' </summary> ''' <typeparam name="TKey">The type of the keys in the dictionary.</typeparam> ''' <typeparam name="TValue">The type of the values in the dictionary.</typeparam> Public Class NamePendingDictionary(Of TKey, TValue) Inherits Dictionary(Of TKey, TValue) Delegate Function DefaultValue() As TValue ''' <summary> ''' Gets or sets the value associated with the specified key. If the specified key does not exist ''' then <paramref name="createDefaultValue"/> is invoked and added to the dictionary. The created ''' value is then returned. ''' </summary> ''' <param name="key">The key of the value to get.</param> ''' <param name="createDefaultValue"> ''' The delegate to invoke if <paramref name="key"/> does not exist in the dictionary. ''' </param> ''' <exception cref="T:System.ArgumentNullException"><paramref name="key" /> is null.</exception> Default Public Overloads ReadOnly Property Item(ByVal key As TKey, ByVal createDefaultValue As DefaultValue) As TValue Get Dim value As TValue If createDefaultValue Is Nothing Then Throw New ArgumentNullException("createValue") End If If Not Me.TryGetValue(key, value) Then value = createDefaultValue.Invoke() Me.Add(key, value) End If Return value End Get End Property End Class

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