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Search found 1919 results on 77 pages for 'typeof'.

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  • Reflective Generic Detection

    - by Aren B
    Trying to find out if a provided Type is of a given generic type (with any generic types inside) Let me Explain: bool IsOfGenericType(Type baseType, Type sampleType) { /// ... } Such that: IsOfGenericType(typeof(Dictionary<,>), typeof(Dictionary<string, int>)); // True IsOfGenericType(typeof(IDictionary<,>), typeof(Dictionary<string, int>)); // True IsOfGenericType(typeof(IList<>), typeof(Dictionary<string,int>)); // False However, I played with some reflection in the intermediate window, here were my results: typeof(Dictionary<,>) is typeof(Dictionary<string,int>) Type expected typeof(Dictionary<string,int>) is typeof(Dictionary<string,int>) Type expected typeof(Dictionary<string,int>).IsAssignableFrom(typeof(Dictionary<,>)) false typeof(Dictionary<string,int>).IsSubclassOf(typeof(Dictionary<,>)) false typeof(Dictionary<string,int>).IsInstanceOfType(typeof(Dictionary<,>)) false typeof(Dictionary<,>).IsInstanceOfType(typeof(Dictionary<string,int>)) false typeof(Dictionary<,>).IsAssignableFrom(typeof(Dictionary<string,int>)) false typeof(Dictionary<,>).IsSubclassOf(typeof(Dictionary<string,int>)) false typeof(Dictionary<,>) is typeof(Dictionary<string,int>) Type expected typeof(Dictionary<string,int>) is typeof(Dictionary<string,int>) Type expected typeof(Dictionary<string,int>).IsAssignableFrom(typeof(Dictionary<,>)) false typeof(Dictionary<string,int>).IsSubclassOf(typeof(Dictionary<,>)) false typeof(Dictionary<string,int>).IsInstanceOfType(typeof(Dictionary<,>)) false typeof(Dictionary<,>).IsInstanceOfType(typeof(Dictionary<string,int>)) false typeof(Dictionary<,>).IsAssignableFrom(typeof(Dictionary<string,int>)) false typeof(Dictionary<,>).IsSubclassOf(typeof(Dictionary<string,int>)) false So now I'm at a loss because when you look at the base.Name on typeof(Dictionary) you get Dictionary`2 Which is the same as typeof(Dictionary<,>).Name

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  • Smart way to find the corresponding nullable type?

    - by Marc Wittke
    How could I avoid this dictionary (or create it dynamically)? Dictionary<Type,Type> CorrespondingNullableType = new Dictionary<Type, Type> { {typeof(bool), typeof(bool?)}, {typeof(byte), typeof(byte?)}, {typeof(sbyte), typeof(sbyte?)}, {typeof(char), typeof(char?)}, {typeof(decimal), typeof(decimal?)}, {typeof(double), typeof(double?)}, {typeof(float), typeof(float?)}, {typeof(int), typeof(int?)}, {typeof(uint), typeof(uint?)}, {typeof(long), typeof(long?)}, {typeof(ulong), typeof(ulong?)}, {typeof(short), typeof(short?)}, {typeof(ushort), typeof(ushort?)}, {typeof(Guid), typeof(Guid?)}, };

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  • C#/.NET Little Wonders: Use Cast() and TypeOf() to Change Sequence Type

    - 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. We’ve seen how the Select() extension method lets you project a sequence from one type to a new type which is handy for getting just parts of items, or building new items.  But what happens when the items in the sequence are already the type you want, but the sequence itself is typed to an interface or super-type instead of the sub-type you need? For example, you may have a sequence of Rectangle stored in an IEnumerable<Shape> and want to consider it an IEnumerable<Rectangle> sequence instead.  Today we’ll look at two handy extension methods, Cast<TResult>() and OfType<TResult>() which help you with this task. Cast<TResult>() – Attempt to cast all items to type TResult So, the first thing we can do would be to attempt to create a sequence of TResult from every item in the source sequence.  Typically we’d do this if we had an IEnumerable<T> where we knew that every item was actually a TResult where TResult inherits/implements T. For example, assume the typical Shape example classes: 1: // abstract base class 2: public abstract class Shape { } 3:  4: // a basic rectangle 5: public class Rectangle : Shape 6: { 7: public int Widtgh { get; set; } 8: public int Height { get; set; } 9: } And let’s assume we have a sequence of Shape where every Shape is a Rectangle… 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: // ... 6: }; To get the sequence of Shape as a sequence of Rectangle, of course, we could use a Select() clause, such as: 1: // select each Shape, cast it to Rectangle 2: var rectangles = shapes 3: .Select(s => (Rectangle)s) 4: .ToList(); But that’s a bit verbose, and fortunately there is already a facility built in and ready to use in the form of the Cast<TResult>() extension method: 1: // cast each item to Rectangle and store in a List<Rectangle> 2: var rectangles = shapes 3: .Cast<Rectangle>() 4: .ToList(); However, we should note that if anything in the list cannot be cast to a Rectangle, you will get an InvalidCastException thrown at runtime.  Thus, if our Shape sequence had a Circle in it, the call to Cast<Rectangle>() would have failed.  As such, you should only do this when you are reasonably sure of what the sequence actually contains (or are willing to handle an exception if you’re wrong). Another handy use of Cast<TResult>() is using it to convert an IEnumerable to an IEnumerable<T>.  If you look at the signature, you’ll see that the Cast<TResult>() extension method actually extends the older, object-based IEnumerable interface instead of the newer, generic IEnumerable<T>.  This is your gateway method for being able to use LINQ on older, non-generic sequences.  For example, consider the following: 1: // the older, non-generic collections are sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 13 }, 5: new Rectangle { Width = 10, Height = 20 }, 6: // ... 7: }; Since this is an older, object based collection, we cannot use the LINQ extension methods on it directly.  For example, if I wanted to query the Shape sequence for only those Rectangles whose Width is > 5, I can’t do this: 1: // compiler error, Where() operates on IEnumerable<T>, not IEnumerable 2: var bigRectangles = shapes.Where(r => r.Width > 5); However, I can use Cast<Rectangle>() to treat my ArrayList as an IEnumerable<Rectangle> and then do the query! 1: // ah, that’s better! 2: var bigRectangles = shapes.Cast<Rectangle>().Where(r => r.Width > 5); Or, if you prefer, in LINQ query expression syntax: 1: var bigRectangles = from s in shapes.Cast<Rectangle>() 2: where s.Width > 5 3: select s; One quick warning: Cast<TResult>() only attempts to cast, it won’t perform a cast conversion.  That is, consider this: 1: var intList = new List<int> { 1, 1, 2, 3, 5, 8, 13, 21, 34, 55, 89 }; 2:  3: // casting ints to longs, this should work, right? 4: var asLong = intList.Cast<long>().ToList(); Will the code above work?  No, you’ll get a InvalidCastException. Remember that Cast<TResult>() is an extension of IEnumerable, thus it is a sequence of object, which means that it will box every int as an object as it enumerates over it, and there is no cast conversion from object to long, and thus the cast fails.  In other words, a cast from int to long will succeed because there is a conversion from int to long.  But a cast from int to object to long will not, because you can only unbox an item by casting it to its exact type. For more information on why cast-converting boxed values doesn’t work, see this post on The Dangers of Casting Boxed Values (here). OfType<TResult>() – Filter sequence to only items of type TResult So, we’ve seen how we can use Cast<TResult>() to change the type of our sequence, when we expect all the items of the sequence to be of a specific type.  But what do we do when a sequence contains many different types, and we are only concerned with a subset of a given type? For example, what if a sequence of Shape contains Rectangle and Circle instances, and we just want to select all of the Rectangle instances?  Well, let’s say we had this sequence of Shape: 1: var shapes = new List<Shape> 2: { 3: new Rectangle { Width = 3, Height = 5 }, 4: new Rectangle { Width = 10, Height = 13 }, 5: new Circle { Radius = 10 }, 6: new Square { Side = 13 }, 7: // ... 8: }; Well, we could get the rectangles using Select(), like: 1: var onlyRectangles = shapes.Where(s => s is Rectangle).ToList(); But fortunately, an easier way has already been written for us in the form of the OfType<T>() extension method: 1: // returns only a sequence of the shapes that are Rectangles 2: var onlyRectangles = shapes.OfType<Rectangle>().ToList(); Now we have a sequence of only the Rectangles in the original sequence, we can also use this to chain other queries that depend on Rectangles, such as: 1: // select only Rectangles, then filter to only those more than 2: // 5 units wide... 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); The OfType<Rectangle>() will filter the sequence to only the items that are of type Rectangle (or a subclass of it), and that results in an IEnumerable<Rectangle>, we can then apply the other LINQ extension methods to query that list further. Just as Cast<TResult>() is an extension method on IEnumerable (and not IEnumerable<T>), the same is true for OfType<T>().  This means that you can use OfType<TResult>() on object-based collections as well. For example, given an ArrayList containing Shapes, as below: 1: // object-based collections are a sequence of object 2: var shapes = new ArrayList 3: { 4: new Rectangle { Width = 3, Height = 5 }, 5: new Rectangle { Width = 10, Height = 13 }, 6: new Circle { Radius = 10 }, 7: new Square { Side = 13 }, 8: // ... 9: }; We can use OfType<Rectangle> to filter the sequence to only Rectangle items (and subclasses), and then chain other LINQ expressions, since we will then be of type IEnumerable<Rectangle>: 1: // OfType() converts the sequence of object to a new sequence 2: // containing only Rectangle or sub-types of Rectangle. 3: var onlyBigRectangles = shapes.OfType<Rectangle>() 4: .Where(r => r.Width > 5) 5: .ToList(); Summary So now we’ve seen two different ways to get a sequence of a superclass or interface down to a more specific sequence of a subclass or implementation.  The Cast<TResult>() method casts every item in the source sequence to type TResult, and the OfType<TResult>() method selects only those items in the source sequence that are of type TResult. You can use these to downcast sequences, or adapt older types and sequences that only implement IEnumerable (such as DataTable, ArrayList, etc.). Technorati Tags: C#,CSharp,.NET,LINQ,Little Wonders,TypeOf,Cast,IEnumerable<T>

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  • When iterating over values, why does typeof(value) return "string" when value is a number? Javascrip

    - by Mark
    I'm using Google Chrome for this test: Contrary to intuition, the first loop alerts "string" 3 times, while the second loop alerts "number" 3 times. numarray = [1, 2, 3]; //for-each loop for(num in numarray) alert(typeof(num)); //standard loop for(i=0; i<numarray.length; i++) alert(typeof(numarray[i])); I was expecting both loops to alert "number" 3 times. How is the first loop implemented in Javascript? In other words, if the for-each is syntactic sugar, what is its equivalent using a standard loop? Also, is there some way to iterate over an object's namespace using a standard loop? I'm looking to touch every one of some object's methods and attributes using a loop of the second kind. I'm new to Javascript and any help is highly appreciated, thanks.

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  • No-argument method on window.external is invoked when checking with typeof

    - by janko
    Hi, I am trying to display an HTML page with embedded JavaScript code inside a System.Windows.Forms.WebBrowser control. The JavaScript code is expected to interact with the embedding environment through the window.external object. Before invoking a method on window.external, JavaScript is supposed to check for the existance of the method. If it is not there, the code should invoke a generic fallback method. // basic idea if (typeof(window.external.MyMethod) != 'undefined') { window.external.MyMethod(args); } else { window.external.Generic("MyMethod", args); } However, checking for a no-argument method with typeof seems to invoke the method already. That is, if MyMethod accepts any positive number of arguments, the code above will work perfectly; but, if MyMethod is a no-argument method, then the expression typeof(window.external.MyMethod) will not check for its type but invoke it, too. Is there any work-around to this behavior? Can I somehow escape the expression window.external.MyMethod to prevent the method call from occurring?

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  • typeof for html plugin elements

    - by gf
    When using ECMAScripts typeof on plugin elements (i.e. embed or object), Safari & FireFox return "function": typeof(window.document['myPlugin']) // "function" This can't be influenced on the plugin side, as the browser doesn't call the plugin here. Funny enough, in IE the same line evaluates to "object". Is that simply implementation dependent behaviour as per ECMAScript §11.4.3 or am i missing something here?

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  • Javascript instanceof & typeof in GWT (JSNI)

    - by rybz
    Hi, I've encountered an curious problem while trying to use some objects through JSNI in GWT. Let's say we have javscript file with the function defined: test.js: function test(arg){ var type = typeof(arg); if (arg instanceof Array) alert('Array'); if (arg instanceof Object) alert('Object'); if (arg instanceof String) alert('String'); } And the we want to call this function user JSNI: public static native void testx()/ *-{ $wnd.test( new Array(1, 2, 3) ); $wnd.test( [ 1, 2, 3 ] ); $wnd.test( {val:1} ); $wnd.test( "Some text" ); }-*/; The questions are: why instanceof instructions will always return false? why typeof will always return "object" ? how to pass these objects so that they were recognized properly?

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  • F# equivalent of the C# typeof(IEnumerable<>)

    - by Rune FS
    I have a piece of code where I need to figure out if a given type implements IEnumerable (I don't care about the T) I've tried (t:System.Type in case you wonder) let interfaces = t.GetInterfaces() let enumerbale = interfaces.Any( fun t -> (t.GetGenericTypeDefinition() = typeof<IEnumerable<>>) however that wont compile (the compile don't like the <). I then tried let interfaces = t.GetInterfaces() let enumerbale = interfaces.Any( fun t -> (t.GetGenericTypeDefinition() = typeof<IEnumerable<'a>>) but get's a warning that 'a is constraint to obj. I Don't want to figure out if IEnumerable is implemented but IEnumerabl<. Any one know's the solution and btw feel free to comment on the code above as well. It's my first non-trivial F# program

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  • WCF : FaultContract(typeof(ExceptionDetail)) issue

    - by jitus
    I have put the attribute [FaultContract(typeof(ExceptionDetail))] for my operation contract. When I am trying to add the service th' a client app, I get this error - "Custom tool error: Failed to generate code for the service reference 'ServiceReference1'. Please check other error and warning messages for details." But when I comment out the FaultContract Attribute, I am able to add the wcf service reference th' my client app. Would appreciate if somebody can help me solve this mystery. Thanks

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  • Why does typeof NaN return 'number'?

    - by KooiInc
    Just out of curiosity. It doesn't seem very logical that typeof NaN is number. Just like NaN === NaN or NaN == NaN returning false, by the way. Is this one of the peculiarities of javascript, or would there be a reason for this?

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  • decltype, result_of, or typeof?

    - by Neil G
    I have: class A { public: B toCPD() const; And: template<typename T> class Ev { public: typedef result_of(T::toCPD()) D; After instantiating Ev<A>, the compiler says: meta.h:12: error: 'T::toCPD' is not a type neither decltype nor typeof work either.

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  • C# equivalent of typeof for fields

    - by rwallace
    With reflection, you can look up a class from a string at run time, but you can also say typeof(Foo) and get compile time type checking, auto completion etc. If what you want is a field not a class, you can look it up from a string at runtime, but if you want compile time type checking etc., is there anyway to say something like fieldof(Foo.Bar)? I know the name of both the class and the field in advance, and I want to be able to refer to the field at compile time rather than with a run-time string lookup.

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  • alert(line) alerts 'ac' and typeof(line) is 'string', but charAt is not a function

    - by Delirium tremens
    alert(line) alerts 'ac' typeof(line) is 'string' When I run line.charAt(0), charAt is not a function. When line is 'http://www.google.com/', it works, I think it's the UTF-8 encoding of the file that I opened... How to make charAt work with UTF-8? UPDATED: http://mxr.mozilla.org/mozilla-central/source/netwerk/dns/src/effective_tld_names.dat?raw=1 is in my extension's chrome folder as effective_tld_names.dat To run the code: authority = 'orkut.com.br'; lines = sc_geteffectivetldnames(); lines = sc_preparetouse(lines); domainname = sc_extractdomainname(authority, lines); The code: function sc_geteffectivetldnames () { var MY_ID = "[email protected]"; var em = Components.classes["@mozilla.org/extensions/manager;1"]. getService(Components.interfaces.nsIExtensionManager); var file = em.getInstallLocation(MY_ID).getItemFile(MY_ID, "chrome/effective_tld_names.dat"); var istream = Components.classes["@mozilla.org/network/file-input-stream;1"]. createInstance(Components.interfaces.nsIFileInputStream); istream.init(file, 0x01, 0444, 0); istream.QueryInterface(Components.interfaces.nsILineInputStream); var line = {}, lines = [], hasmore; do { hasmore = istream.readLine(line); lines.push(line.value); } while(hasmore); istream.close(); return lines; } function sc_preparetouse(lines) { lines = sc_notcomment(lines); lines = sc_notempty(lines); return lines; } function sc_notcomment(lines) { var line; var commentre; var matchedcomment; var replacedlines; replacedlines = new Array(); var i = 0; while (i < lines.length) { line = lines[i]; commentre = new RegExp("^//", 'i'); matchedcomment = line.match(commentre); if(matchedcomment) { lines.splice(i, 1); } else { i++; } } return lines; } function sc_notempty(lines) { var line; var emptyre; var matchedempty; var replacedlines; replacedlines = new Array(); var i = 0; while (i < lines.length) { line = lines[i]; emptyre = new RegExp("^$", 'i'); matchedempty = line.match(emptyre); if(matchedempty) { lines.splice(i, 1); } else { i++; } } return lines; } function sc_extractdomainname(authority, lines) { for (var i = 0; i < lines.length; i++) { line = lines[i]; alert(line); alert(typeof(line)); if (line.chatAt(0) == '*') { alert('test1'); continue; } if (line.chatAt(0) == '!') { alert('test2'); line.chatAt(0) = ''; } alert('test3'); checkline = sc_checknotasteriskline(authority, line); if (checkline) { domainname = checkline; } } if (!domainname) { for (var i = 0; i < lines.length; i++) { line = lines[i]; alert(line); if (line.chatAt(0) != '*') { continue; alert('test4'); } if (line.chatAt(0) == '!') { line.chatAt(0) = ''; alert('test5'); } alert('test6'); checkline = sc_checkasteriskline(authority, line); if (checkline) { domainname = checkline; } } } return domainname; } It alerts 'ac', then 'string', then nothing.

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  • alert(line) alerts 'ac' and typeof(line) is 'string', but charAt is not a function

    - by Delirium tremens
    alert(line) alerts 'ac' typeof(line) is 'string' When I run line.charAt(0), charAt is not a function. When line is 'http://www.google.com/', it works, I think it's the UTF-8 encoding of the file that I opened... How to make charAt work with UTF-8? UPDATED: http://mxr.mozilla.org/mozilla-central/source/netwerk/dns/src/effective_tld_names.dat?raw=1 is in my extension's chrome folder as effective_tld_names.dat To run the code: authority = 'orkut.com.br'; lines = sc_geteffectivetldnames(); lines = sc_preparetouse(lines); domainname = sc_extractdomainname(authority, lines); The code: function sc_geteffectivetldnames () { var MY_ID = "[email protected]"; var em = Components.classes["@mozilla.org/extensions/manager;1"]. getService(Components.interfaces.nsIExtensionManager); var file = em.getInstallLocation(MY_ID).getItemFile(MY_ID, "chrome/effective_tld_names.dat"); var istream = Components.classes["@mozilla.org/network/file-input-stream;1"]. createInstance(Components.interfaces.nsIFileInputStream); istream.init(file, 0x01, 0444, 0); istream.QueryInterface(Components.interfaces.nsILineInputStream); var line = {}, lines = [], hasmore; do { hasmore = istream.readLine(line); lines.push(line.value); } while(hasmore); istream.close(); return lines; } function sc_preparetouse(lines) { lines = sc_notcomment(lines); lines = sc_notempty(lines); return lines; } function sc_notcomment(lines) { var line; var commentre; var matchedcomment; var replacedlines; replacedlines = new Array(); var i = 0; while (i < lines.length) { line = lines[i]; commentre = new RegExp("^//", 'i'); matchedcomment = line.match(commentre); if(matchedcomment) { lines.splice(i, 1); } else { i++; } } return lines; } function sc_notempty(lines) { var line; var emptyre; var matchedempty; var replacedlines; replacedlines = new Array(); var i = 0; while (i < lines.length) { line = lines[i]; emptyre = new RegExp("^$", 'i'); matchedempty = line.match(emptyre); if(matchedempty) { lines.splice(i, 1); } else { i++; } } return lines; } function sc_extractdomainname(authority, lines) { for (var i = 0; i < lines.length; i++) { line = lines[i]; alert(line); alert(typeof(line)); if (line.chatAt(0) == '*') { alert('test1'); continue; } if (line.chatAt(0) == '!') { alert('test2'); line.chatAt(0) = ''; } alert('test3'); checkline = sc_checknotasteriskline(authority, line); if (checkline) { domainname = checkline; } } if (!domainname) { for (var i = 0; i < lines.length; i++) { line = lines[i]; alert(line); if (line.chatAt(0) != '*') { alert('test4'); continue; } if (line.chatAt(0) == '!') { alert('test5'); line.chatAt(0) = ''; } alert('test6'); checkline = sc_checkasteriskline(authority, line); if (checkline) { domainname = checkline; } } } return domainname; } It alerts 'ac', then 'string', then nothing.

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  • typeof === "undefined" vs. != null

    - by Thor Thurn
    I often see JavaScript code which checks for undefined parameters etc. this way: if (typeof input !== "undefined") { // do stuff } This seems kind of wasteful, since it involves both a type lookup and a string comparison, not to mention its verbosity. It's needed because 'undefined' could be renamed, though. My question is: How is that code any better than this approach: if (input != null) { // do stuff } As far as I know, you can't redefine null, so it's not going to break unexpectedly. And, because of the type-coercion of the != operator, this checks for both undefined and null... which is often exactly what you want (e.g. for optional function parameters). Yet this form does not seem widespread, and it even causes JSLint to yell at you for using the evil != operator. Why is this considered bad style?

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  • How to get exactly typeof is object/array/null..?

    - by 3gwebtrain
    var obj = {},ar = [],nothing=null,empty=undefined,word ='string',headorTail = true; console.log(typeof obj) //object console.log(typeof ar)//object console.log(typeof nothing)//object console.log(typeof empty)//undefined console.log(typeof word)//string console.log(typeof headorTail)//boolean But how can i get the type of obj,ar,nothing as "object, array,null" - what is the best way to achieve this?

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  • Macro to improve callback registration readability

    - by Warren Seine
    I'm trying to write a macro to make a specific usage of callbacks in C++ easier. All my callbacks are member functions and will take this as first argument and a second one whose type inherits from a common base class. The usual way to go is: register_callback(boost::bind(&my_class::member_function, this, _1)); I'd love to write: register_callback(HANDLER(member_function)); Note that it will always be used within the same class. Even if typeof is considered as a bad practice, it sounds like a pretty solution to the lack of __class__ macro to get the current class name. The following code works: typedef typeof(*this) CLASS; boost::bind(& CLASS :: member_function, this, _1)(my_argument); but I can't use this code in a macro which will be given as argument to register_callback. I've tried: #define HANDLER(FUN) \ boost::bind(& typeof(*this) :: member_function, this, _1); which doesn't work for reasons I don't understand. Quoting GCC documentation: A typeof-construct can be used anywhere a typedef name could be used. My compiler is GCC 4.4, and even if I'd prefer something standard, GCC-specific solutions are accepted.

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  • Typechecking macro arguments in C

    - by Rocketmagnet
    Hi all, Is is possible to typecheck arguments to a #define macro? For example: typedef enum { REG16_A, REG16_B, REG16_C }REG16; #define read_16(reg16) read_register_16u(reg16); \ assert(typeof(reg16)==typeof(REG16)); The above code doesn't seem to work. What am I doing wrong? BTW, I am using gcc, and I can guarantee that I will always be using gcc in this project. The code does not need to be portable.

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  • C# 4.0: Covariance And Contravariance In Generics Made Easy

    - by Paulo Morgado
    In my last post, I went through what is variance in .NET 4.0 and C# 4.0 in a rather theoretical way. Now, I’m going to try to make it a bit more down to earth. Given: class Base { } class Derived : Base { } Such that: Trace.Assert(typeof(Base).IsClass && typeof(Derived).IsClass && typeof(Base).IsGreaterOrEqualTo(typeof(Derived))); Covariance interface ICovariantIn<out T> { } Trace.Assert(typeof(ICovariantIn<Base>).IsGreaterOrEqualTo(typeof(ICovariantIn<Derived>))); Contravariance interface ICovariantIn<out T> { } Trace.Assert(typeof(IContravariantIn<Derived>).IsGreaterOrEqualTo(typeof(IContravariantIn<Base>))); Invariance interface IInvariantIn<T> { } Trace.Assert(!typeof(IInvariantIn<Base>).IsGreaterOrEqualTo(typeof(IInvariantIn<Derived>)) && !typeof(IInvariantIn<Derived>).IsGreaterOrEqualTo(typeof(IInvariantIn<Base>))); Where: public static class TypeExtensions { public static bool IsGreaterOrEqualTo(this Type self, Type other) { return self.IsAssignableFrom(other); } }

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  • Declare variables that depend on unknown type in template functions.

    - by rem
    Suppose I'm writing a template function foo that has type parameter T. It gets an object of type T that must have method bar(). And inside foo I want to create a vector of objects of type returned by bar. In GNU C++ I can write something like that: template<typename T> void foo(T x) { std::vector<__typeof(x.bar())> v; v.push_back(x.bar()); v.push_back(x.bar()); v.push_back(x.bar()); std::cout << v.size() << std::endl; } How to do the same thing in Microsoft Visual C++? Is there some way to write this code that works in both GNU C++ and Visual C++?

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