When I'm trying to use params in an Action delegate...
private Action<string, params object[]> WriteToLogCallBack; I received this design time error:
Invalid token 'params' in class, struct, or interface member declaration
Any help!
5 Answers
How about this workaround?
private Action<string, object[]> writeToLogCallBack; public void WriteToLogCallBack(string s, params object[] args) { if(writeToLogCallBack!=null) writeToLogCallBack(s,args); } Or you could define your own delegate type:
delegate void LogAction(string s, params object[] args); 
1 Comment
toddmo
How do you call this with a lambda?
Variadic type parameters are not possible in C#.
That's why there're many declarations for Action<...>, Func<...>, and Tuple<...>, for example. It would be an interesting feature, though. C++0x has them.
1 Comment
CodesInChaos
Not sure how well it would work with generics (as opposed to templates).
You could try this. It allows for any number of arguments, and you'll get a compile time error if you pass the wrong number or type of arguments.
public delegate T ParamsAction<T>(params object[] oArgs); public static T LogAction<T>(string s, ParamsAction<T> oCallback) { Log(s); T result = oCallback(); return result; } Foo foo = LogAction<Foo>("Hello world.", aoArgs => GetFoo(1,"",'',1.1)); 
4 Comments
Gwasshoppa
This is a really nice way of doing it... Nice work sir
kamgman
Awesome piece of code here Bryan. I have added below a minor extension to the above code to show how to wrap multiple method calls. I am using this to wrap multiple methods that contain database calls, into a single transaction. Thanks Bryan :-)
Mark Lauter
Was this supposed to return result instead of T?
Philipp Munin
what's the point of it if you cannot do
LogAction<Foo>("Hello world.", (p1,p2,p3) => GetFoo(p1,p2,p3));??? minusing....You can use params in the actual declaration of a delegate, but not in type of one. The generic parameters to an Action are only types, not the actual arguments to be passed when invoking the delegate. params is not a type, it is a keyword.
answered Oct 30, 2010 at 16:50
Gordon Gustafson
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Comments
I have done a minor extension to the above code from Bryan, to show how to wrap multiple method calls.
I am using this to wrap multiple methods that contain database calls, into a single transaction.
Thanks Bryan :-)
(You can run the following in LINQPad to test)
//Wrapper code public delegate void MyAction(params object[] objArgs); public static void RunActions(params MyAction[] actnArgs) { Console.WriteLine("WrapperBefore: Begin transaction code\n"); actnArgs.ToList().ForEach( actn => actn() ); Console.WriteLine("\nWrapperAfter: Commit transaction code"); } //Methods being called public void Hash (string s, int i, int j) => Console.WriteLine(" Hash-method call: " + s + "###" + i.ToString() + j.ToString()); public void Slash (int i, string s) => Console.WriteLine(" Slash-method call: " + i.ToString()+ @"////" + s); //Actual calling code void Main() { RunActions( objArgs => Hash("One", 2, 1) ,objArgs => Slash(3, "four") ); } //Resulting output: // // WrapperBefore: Begin transaction code // // Hash-method call: One###21 // Slash-method call: 3////four // // WrapperAfter: Commit transaction code 
refin type definition?