In C# use the Delegate class to invoke a constructor

Question

There is a method defined like so:

public static void MyMethod(Delegate action, parames object[] parameters)
{
   action.DynamicInvoke(parameters);
   //Do something
}

So far this method works very well to receive all kinds of method and functions with any number of parameters but I was wondering if there is a way to pass a constructor as the Delegate parameter.

Thank you for your help.

Someone was trying to do this [with this question](http://stackoverflow.com/questions/15771653/delegate-for-any-method-type-c-sharp/15771977), and I think taking the Funct (or in this case, Action) is much more readable, and enforces type safety and encapsulation. — IdeaHat, Apr 04 '13 at 14:54
@JonSkeet: Hi Jon. Yes that is what I meant. Thanks to point it out. — Sergio Romero, Apr 04 '13 at 16:08

score 8 · Accepted Answer · edited Apr 04 '13 at 20:53

8

You will have to construct an anonymous function around the constructor, as constructors cannot be converted to delegates directly. (This is because the constructor is not what actually creates an object; the newobj instruction creates the object and then calls the constructor to initialize the allocated memory. Creating a delegate for a constructor directly would be the equivalent of a call instruction, and that doesn't make sense for constructors.)

For example, given this type:

class Foo {
    public Foo(string str) { }
}

You could do this:

MyMethod(new Func<string, Foo>(str => new Foo(str)), "a string");

edited Apr 04 '13 at 20:53

Sergio Romero

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answered Apr 04 '13 at 14:42

cdhowie

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1

+1 for a fantastic answer that leverages the current method. I was pretty sure the only way was `Activator.CreateInstance`. – Mike Perrenoud Apr 04 '13 at 17:07
@cdhowie: It does not seem to like it. I am trying it with MyMethod((x, y) => new MyObject(x, y), objectOne, objectTwo) and the compiler says "Argument type 'lambda expression' is not assignable to parameter type 'System.Delegate' – Sergio Romero Apr 04 '13 at 17:31
@cdhowie: I took the liberty of making a very small correction to the answer and that makes it exactly what I was looking for. Thank you! – Sergio Romero Apr 04 '13 at 20:50

Mike Perrenoud · Answer 2 · 2013-04-04T17:07:54.113

1

As cdhowie showed you, it is possible with your current method, but another option if necessary is to leverage Activator.CreateInstance, so it might look something like this:

public static object CreateObject(Type t, params object[] parameters)
{
    return Activator.CreateInstance(t, parameters);
}

edited Apr 04 '13 at 17:07

answered Apr 04 '13 at 14:43

Mike Perrenoud

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In C# use the Delegate class to invoke a constructor

2 Answers2