Is it possible to use ref types in C# built-in Action<> delegate?

C# has built-in delegates Action<> and Func<>. Is it possible to use 'ref' type parameters for this delegates? For example, this code:

public deleg开发者_JS百科ate void DTest( ref Guid a );
public event DTest ETest;

Will compile. But if I use Action<>, it will not compile:

public event Action< ref Guid > ETest;

Any hints?

No, you can't use pass-by-reference with the Action delegates. While there is a concept of "type passed by reference" as a Type in the framework, it's not really a type in the normal sense as far as C# is concerned. ref is a modifier for the parameter, not part of the type name, if you see what I mean.

However, you can build your own set of equivalent types, e.g.

delegate void ActionRef<T>(ref T item);

Of course, if you want a mixture of ref and non-ref parameters in the same delegate, you get into a horrible set of combinations:

delegate void ActionRef1<T1, T2>(ref T1 arg1, T2 arg2);
delegate void ActionRef2<T1, T2>(T1 arg1, ref T2 arg2);
delegate void ActionRef3<T1, T2>(ref T1 arg1, ref T2 arg2);

You can as long as your reference is a complex object (has properties).

Example object:

public class MyComplexObject
{
    /// <summary>
    /// Name provided for the result.
    /// </summary>
    public string Name { get; set; }

    /// <summary>
    /// Value of the result.
    /// </summary>
    public object Value { get; set; }
}

Used in an Action:

Action<MyComplexObject> myAction = (MyComplexObject result) =>
{
    result.Value = MyMethodThatReturnsSomething();                                              
};

Since the MyComplexObject reference is not changed, the data is preserved.

Also posted on my blog.