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  • Overload Resolution and Optional Arguments in C# 4

    - by Dale McCoy
    I am working with some code that has seven overloads of a function TraceWrite: void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, bool LogToFileOnly, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string PieceID, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, LogWindowCommandENUM LogWindowCommand, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, bool UserMessage, int UserMessagePercent, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, string PieceID, LogWindowCommandENUM LogWindowCommand, string Data = ""); void TraceWrite(string Application, LogLevelENUM LogLevel, string Message, LogWindowCommandENUM LogWindowCommand, bool UserMessage, int UserMessagePercent, string Data = ""); (All public static, namespacing noise elided above and throughout.) So, with that background: 1) Elsewhere, I call TraceWrite with four arguments: string, LogLevelENUM, string, bool, and I get the following errors: error CS1502: The best overloaded method match for 'TraceWrite(string, LogLevelENUM, string, string)' has some invalid arguments error CS1503: Argument '4': cannot convert from 'bool' to 'string' Why doesn't this call resolve to the second overload? (TraceWrite(string, LogLevelENUM, string, bool, string = "")) 2) If I were to call TraceWrite with string, LogLevelENUM, string, string, which overload would be called? The first or the third? And why?

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  • Optional non-system type parameters

    - by Courtney de Lautour
    C#4.0 obviously brings optional parameters (which I've been waiting for, for quite some time). However it seems that because only system types can be const that I cannot use any class/struct which I have created, as an optional param. Is there a some way which allows me to use a more complex type as an optional parameter. Or is this one of the realities that one must just live with?

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  • How to make a parameter optional in WSDL?

    - by user305069
    I have a WebService API which needs 2 of its parameters to be optional in the WSDL public wsProxy[] Insert(wsProxy[] proxies, string loginname, string password, bool returnNewData) { //code here } I need to a way to show loginname and password as optional in the WSDL. Is there any way to do this in C#. Can I maybe add an tag in front of the parameters like this [optional]loginname? I have been looking around but haven't been able to find anything so far.

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  • HTML: Include, or exclude, optional closing tags?

    - by Ian Boyd
    Some HTML1 closing tags are optional, i.e.: </HTML> </HEAD> </BODY> </P> </DT> </DD> </LI> </OPTION> </THEAD> </TH> </TBODY> </TR> </TD> </TFOOT> </COLGROUP> Note: Not to be confused with closing tags that are forbidden to be included, i.e.: </IMG> </INPUT> </BR> </HR> </FRAME> </AREA> </BASE> </BASEFONT> </COL> </ISINDEX> </LINK> </META> </PARAM> Note: xhtml is different from HTML. xhtml is a form of xml, which requires every element have a closing tag. A closing tag can be forbidden in html, yet mandatory in xhtml. Are the optional closing tags ideally included, but we'll accept them if you forgot them, or ideally not included, but we'll accept them if you put them in In other words, should i include them, or should i not include them? The HTML 4.01 spec talks about closing element tags being optional, but doesn't say if it's preferable to include them, or preferable to not include them. On the other hand, a random article on DevGuru says: The ending tag is optional. However, it is recommended that it be included. The reason i ask is because you just know it's optional for compatibility reasons; and they would have made them (mandatory | forbidden) if they could have. Put it another way: What did HTML 1, 2, 3 do with regards to these, now optional, closing tags. What does HTML 5 do? And what should i do? Footnotes 1HTML 4.01

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  • F# Optional Record Field

    - by akaphenom
    I have a F# record type and want one of the fields to be optional: type legComponents = { shares : int<share> ; price : float<dollar / share> ; totalInvestment : float<dollar> ; } type tradeLeg = { id : int ; tradeId : int ; legActivity : LegActivityType ; actedOn : DateTime ; estimates : legComponents ; ?actuals : legComponents ; } in the tradeLeg type I owuld like the the actuals field to be optional. I cant seem to figure it out nor can I seem to find a reliable example on the web. It seem like this sohuld be easy like let ?t : int = None but i realy can't seem to get this to work. Ugh - thank you T

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  • C# 4: conflicting overloaded methods with optional parameters

    - by Thomas
    I have two overloaded methods, one with an optional parameter. void foo(string a) { } void foo(string a, int b = 0) { } now I call: foo("abc"); interestingly the first overload is called. why not the second overload with optional value set to zero? To be honest, I would have expect the compiler to bring an error, at least a warning to avoid unintentional execution of the wrong method. What's the reason for this behaviour? Why did the C# team define it that way? Thanks for your opinions!

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  • Naming Optional Parameters in VSB

    - by SteveNeedsSheetNames
    In Visual Basic, I have Functions with a lot of Optional arguments. I would like to be able to pass just a few of these Optional arguments to a Function without having to use numerous commas and spaces to get to the ones I want. Somewhere I saw a way to name params such as OptVar:=val, but that does not seem to work. Just wondering if there is a way to do this. This would help readability. Thanks in advance for the replies.

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  • Passing optional parameter by reference in c++

    - by Moomin
    I'm having a problem with optional function parameter in C++ What I'm trying to do is to write function with optional parameter which is passed by reference, so that I can use it in two ways (1) and (2), but on (2) I don't really care what is the value of mFoobar. I've tried such a code: void foo(double &bar, double &foobar = NULL) { bar = 100; foobar = 150; } int main() { double mBar(0),mFoobar(0); foo(mBar,mFoobar); // (1) cout << mBar << mFoobar; mBar = 0; mFoobar = 0; foo(mBar); // (2) cout << mBar << mFoobar; return 0; } but it crashes at void foo(double &bar, double &foobar = NULL) with message : error: default argument for 'double& foobar' has type 'int' Is it possible to solve it without function overloading? Thanks in advance for any suggestions. Pawel

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  • Design for object with optional and modifiable attributtes?

    - by Ikuzen
    I've been using the Builder pattern to create objects with a large number of attributes, where most of them are optional. But up until now, I've defined them as final, as recommended by Joshua Block and other authors, and haven't needed to change their values. I am wondering what should I do though if I need a class with a substantial number of optional but non-final (mutable) attributes? My Builder pattern code looks like this: public class Example { //All possible parameters (optional or not) private final int param1; private final int param2; //Builder class public static class Builder { private final int param1; //Required parameters private int param2 = 0; //Optional parameters - initialized to default //Builder constructor public Builder (int param1) { this.param1 = param1; } //Setter-like methods for optional parameters public Builder param2(int value) { param2 = value; return this; } //build() method public Example build() { return new Example(this); } } //Private constructor private Example(Builder builder) { param1 = builder.param1; param2 = builder.param2; } } Can I just remove the final keyword from the declaration to be able to access the attributes externally (through normal setters, for example)? Or is there a creational pattern that allows optional but non-final attributes that would be better suited in this case?

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  • Optional parameters in Visual Studio 2008 Crystal Reports

    - by Andrew
    I am developing a Crystal Report in Visual Studio 2008. I am trying to implement optional parameters so that a user does not have to specify a value or range for a particular field. Essentially, this means there is no filtering done on that field if the user wishes. However, I can't seem to figure out how to do this. Does anyone have any ideas? Let me know if more information is required.

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  • Python constructor does weird things with optional parameters

    - by christangrant
    Can you help me understand of the behaviour and implications of the python __init__ constructor. It seems like when there is an optional parameter and you try and set an existing object to a new object the optional value of the existing object is preserved and copied. Ok that was confusing... so look at an example I concocted below. In the code below I am trying to make a tree structure with nodes and possibly many children . In the first class NodeBad, the constructor has two parameters, the value and any possible children. The second class NodeGood only takes the value of the node as a parameter. Both have an addchild method to add a child to a node. When creating a tree with the NodeGood class, it works as expected. However, when doing the same thing with the NodeBad class, it seems as though a child can only be added once! The code below will result in the following output: Good Tree 1 2 3 [< 3 >] Bad Tree 1 2 2 [< 2 >, < 3 >] Que Pasa? Here is the Example: #!/usr/bin/python class NodeBad: def __init__(self, value, c=[]): self.value = value self.children = c def addchild(self, node): self.children.append(node) def __str__(self): return '< %s >' % self.value def __repr__(self): return '< %s >' % self.value class NodeGood: def __init__(self, value): self.value = value self.children = [] def addchild(self, node): self.children.append(node) def __str__(self): return '< %s >' % self.value def __repr__(self): return '< %s >' % self.value if __name__ == '__main__': print 'Good Tree' ng = NodeGood(1) # Root Node rootgood = ng ng.addchild(NodeGood(2)) # 1nd Child ng = ng.children[0] ng.addchild(NodeGood(3)) # 2nd Child print rootgood.value print rootgood.children[0].value print rootgood.children[0].children[0].value print rootgood.children[0].children print 'Bad Tree' nb = NodeBad(1) # Root Node rootbad = nb nb.addchild(NodeBad(2)) # 1st Child nb = nb.children[0] nb.addchild(NodeBad(3)) # 2nd Child print rootbad.value print rootbad.children[0].value print rootbad.children[0].children[0].value print rootbad.children[0].children

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  • avoiding the tedium of optional parameters

    - by Kyle
    If I have a constructor with say 2 required parameters and 4 optional parameters, how can I avoid writing 16 constructors or even the 10 or so constructors I'd have to write if I used default parameters (which I don't like because it's poor self-documentation)? Are there any idioms or methods using templates I can use to make it less tedious? (And easier to maintain?)

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  • Patterns for simulating optional "out" parameters in C#?

    - by Jesse McGrew
    I'm translating an API from C to C#, and one of the functions allocates a number of related objects, some of which are optional. The C version accepts several pointer parameters which are used to return integer handles to the objects, and the caller can pass NULL for some of the pointers to avoid allocating those objects: void initialize(int *mainObjPtr, int *subObjPtr, int *anotherSubObjPtr); initialize(&mainObj, &subObj, NULL); For the C# version, the obvious translation would use out parameters instead of pointers: public static void Initialize(out int mainObj, out int subObj, out int anotherSubObj); ... but this leaves no way to indicate which objects are unwanted. Are there any well-known examples of C# APIs doing something similar that I could imitate? If not, any suggestions?

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  • Small Python optional arguments question

    - by ooboo
    I have two functions: def f(a,b,c=g(b)): blabla def g(n): blabla c is an optional argument in function f. If the user does not specify its value, the program should compute g(b) and that would be the value of c. But the code does not compile - it says name 'b' is not defined. How to fix that? Someone suggested: def g(b): blabla def f(a,b,c=None): if c is None: c = g(b) blabla But this doesn't work, because maybe the user intended c to be None and then c will have another value.

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  • SQL optional parameters through VB.net

    - by ScaryJones
    I've a document search page with three listboxes that allow multiple selections. They're: Category A Year Category B Only category A is mandatory, the others are optional parameters and might be empty. Each document can belong to multiple options in Category A and multiple options Category B but each document only has one year associated with it. I've kind of got this working through building up a dynamic SQL string but it's messy and I hate using it so I thought I'd ask here if anyone could see an easier way of doing this. An example of the kind of dynamic SQL query i end up with follows: select * from library where libraryID in (select distinct libraryID from categoryAdocs where categoryAdocID in (4)) or year in (2004)

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  • Optional Parameters and Named Arguments in C# 4 (and a cool scenario w/ ASP.NET MVC 2)

    - by ScottGu
    [In addition to blogging, I am also now using Twitter for quick updates and to share links. Follow me at: twitter.com/scottgu] This is the seventeenth in a series of blog posts I’m doing on the upcoming VS 2010 and .NET 4 release. Today’s post covers two new language feature being added to C# 4.0 – optional parameters and named arguments – as well as a cool way you can take advantage of optional parameters (both in VB and C#) with ASP.NET MVC 2. Optional Parameters in C# 4.0 C# 4.0 now supports using optional parameters with methods, constructors, and indexers (note: VB has supported optional parameters for awhile). Parameters are optional when a default value is specified as part of a declaration.  For example, the method below takes two parameters – a “category” string parameter, and a “pageIndex” integer parameter.  The “pageIndex” parameter has a default value of 0, and as such is an optional parameter: When calling the above method we can explicitly pass two parameters to it: Or we can omit passing the second optional parameter – in which case the default value of 0 will be passed:   Note that VS 2010’s Intellisense indicates when a parameter is optional, as well as what its default value is when statement completion is displayed: Named Arguments and Optional Parameters in C# 4.0 C# 4.0 also now supports the concept of “named arguments”.  This allows you to explicitly name an argument you are passing to a method – instead of just identifying it by argument position.  For example, I could write the code below to explicitly identify the second argument passed to the GetProductsByCategory method by name (making its usage a little more explicit): Named arguments come in very useful when a method supports multiple optional parameters, and you want to specify which arguments you are passing.  For example, below we have a method DoSomething that takes two optional parameters: We could use named arguments to call the above method in any of the below ways: Because both parameters are optional, in cases where only one (or zero) parameters is specified then the default value for any non-specified arguments is passed. ASP.NET MVC 2 and Optional Parameters One nice usage scenario where we can now take advantage of the optional parameter support of VB and C# is with ASP.NET MVC 2’s input binding support to Action methods on Controller classes. For example, consider a scenario where we want to map URLs like “Products/Browse/Beverages” or “Products/Browse/Deserts” to a controller action method.  We could do this by writing a URL routing rule that maps the URLs to a method like so: We could then optionally use a “page” querystring value to indicate whether or not the results displayed by the Browse method should be paged – and if so which page of the results should be displayed.  For example: /Products/Browse/Beverages?page=2. With ASP.NET MVC 1 you would typically handle this scenario by adding a “page” parameter to the action method and make it a nullable int (which means it will be null if the “page” querystring value is not present).  You could then write code like below to convert the nullable int to an int – and assign it a default value if it was not present in the querystring: With ASP.NET MVC 2 you can now take advantage of the optional parameter support in VB and C# to express this behavior more concisely and clearly.  Simply declare the action method parameter as an optional parameter with a default value: C# VB If the “page” value is present in the querystring (e.g. /Products/Browse/Beverages?page=22) then it will be passed to the action method as an integer.  If the “page” value is not in the querystring (e.g. /Products/Browse/Beverages) then the default value of 0 will be passed to the action method.  This makes the code a little more concise and readable. Summary There are a bunch of great new language features coming to both C# and VB with VS 2010.  The above two features (optional parameters and named parameters) are but two of them.  I’ll blog about more in the weeks and months ahead. If you are looking for a good book that summarizes all the language features in C# (including C# 4.0), as well provides a nice summary of the core .NET class libraries, you might also want to check out the newly released C# 4.0 in a Nutshell book from O’Reilly: It does a very nice job of packing a lot of content in an easy to search and find samples format. Hope this helps, Scott

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  • preg_match to match an optional string, but not match all of the string

    - by buggedcom
    Take for example the following regex match. preg_match('!^publisher/([A-Za-z0-9\-\_]+)/([0-9]+)/([0-9]{4})-(january|february|march|april|may|june|july|august|september|october|november|december):([0-9]{1,2})-([0-9]{1,2})/([A-Za-z0-9\-\_]+)/([0-9]+)(/page-[0-9]+)?$!', 'publisher/news/1/2010-march:03-23/test_title/1/page-1', $matches); print_r($matches); It produces the following: Array ( [0] => publisher/news/1/2010-march:03-23/test_title/1/page-1 [1] => news [2] => 1 [3] => 2010 [4] => march [5] => 03 [6] => 23 [7] => test_title [8] => 1 [9] => /page-1 ) However as the last match is optional it can also work with matching the following "publisher/news/1/2010-march:03-23/test_title/1". My problem is that I want to be able to match (/page-[0-9]+) if it exists, but match only the page number so "publisher/news/1/2010-march:03-23/test_title/1/page-1" would match like so: Array ( [0] => publisher/news/1/2010-march:03-23/test_title/1/page-1 [1] => news [2] => 1 [3] => 2010 [4] => march [5] => 03 [6] => 23 [7] => test_title [8] => 1 [9] => 1 ) I've tried the following regex '!^publisher/([A-Za-z0-9\-\_]+)/([0-9]+)/([0-9]{4})-(january|february|march|april|may|june|july|august|september|october|november|december):([0-9]{1,2})-([0-9]{1,2})/([A-Za-z0-9\-\_]+)/([0-9]+)/?p?a?g?e?-?([0-9]+)?$!' This works, however it will also match "publisher/news/1/2010-march:03-23/test_title/1/1". I have no idea to perform a match but not have it come back in the matches? Is it possible in a single regex?

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  • C# Adds Optional and Named Arguments

    Earlier this month Microsoft released Visual Studio 2010, the .NET Framework 4.0 (which includes ASP.NET 4.0), and new versions of their core programming languages: C# 4.0 and Visual Basic 10. In designing the latest versions of C# and VB, Microsoft has worked to bring the two languages into closer parity. Certain features available in C# were missing in VB, and vice-a-versa. Last week I wrote about Visual Basic 2010's language enhancements, which include implicit line continuation, auto-implemented properties, and collection initializers - three useful features that were available in previous versions of C#. Similarly, C# 4.0 introduces new features to the C# programming language that were available in earlier versions of Visual Basic, namely optional arguments and named arguments. Optional arguments allow developers to specify default values for one or more arguments to a method. When calling such a method, these optional arguments may be omitted, in which case their default value is used. In a nutshell, optional arguments allow for a more terse syntax for method overloading. Named arguments, on the other hand, improve readability by allowing developers to indicate the name of an argument (along with its value) when calling a method. This article examines how to use optional arguments and named arguments in C# 4.0. Read on to learn more! Read More >

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  • C# Adds Optional and Named Arguments

    Earlier this month Microsoft released Visual Studio 2010, the .NET Framework 4.0 (which includes ASP.NET 4.0), and new versions of their core programming languages: C# 4.0 and Visual Basic 10. In designing the latest versions of C# and VB, Microsoft has worked to bring the two languages into closer parity. Certain features available in C# were missing in VB, and vice-a-versa. Last week I wrote about Visual Basic 2010's language enhancements, which include implicit line continuation, auto-implemented properties, and collection initializers - three useful features that were available in previous versions of C#. Similarly, C# 4.0 introduces new features to the C# programming language that were available in earlier versions of Visual Basic, namely optional arguments and named arguments. Optional arguments allow developers to specify default values for one or more arguments to a method. When calling such a method, these optional arguments may be omitted, in which case their default value is used. In a nutshell, optional arguments allow for a more terse syntax for method overloading. Named arguments, on the other hand, improve readability by allowing developers to indicate the name of an argument (along with its value) when calling a method. This article examines how to use optional arguments and named arguments in C# 4.0. Read on to learn more! Read More >Did you know that DotNetSlackers also publishes .net articles written by top known .net Authors? We already have over 80 articles in several categories including Silverlight. Take a look: here.

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