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The out parameter in C# is used to pass arguments to methods by reference. It differs from the ref keyword in that it does not require parameter variables to be initialized before they are passed to a method.
Func<T, TResult> defines a function that accepts one parameter (of type T) and returns an object (of type TResult).
Func is a delegate that points to a method that accepts one or more arguments and returns a value. Action is a delegate that points to a method which in turn accepts one or more arguments but returns no value. In other words, you should use Action when your delegate points to a method that returns void.
TResult. The type of the return value of the method that this delegate encapsulates. This type parameter is covariant. That is, you can use either the type you specified or any type that is more derived. For more information about covariance and contravariance, see Covariance and Contravariance in Generics.
ref and out are not part of the type parameter definition so you can't use the built-in Func delegate to pass ref and out arguments. Of course, you can declare your own delegate if you want:
delegate V MyDelegate<T,U,V>(T input, out U output);
Why not create a class to encapsulate the results?
public class Result
{
public IList<Foo> List { get; set; }
public Int32 Count { get; set; }
}
The Func family of delegates (or Action for that matter) are nothing but simple delegate types declared like
//.NET 4 and above
public delegate TResult Func<out TResult>()
public delegate TResult Func<in T, out TResult>(T obj)
//.NET 3.5
public delegate TResult Func<T1, T2, TResult>(T1 obj1, T2 obj2)
public delegate TResult Func<T1, T2, T3, TResult>(T1 obj1, T2 obj2, T3 obj3)
etc. Delegates as such can have out/ref parameters, so in your case its only a matter of custom implementation by yourself as other answers have pointed out. As to why Microsoft did not pack this by default, think of the sheer number of combinations it would require.
delegate TResult Func<T1, T2, TResult>(T1 obj1, T2 obj2)
delegate TResult Func<T1, T2, TResult>(out T1 obj1, T2 obj2)
delegate TResult Func<T1, T2, TResult>(T1 obj1, out T2 obj2)
delegate TResult Func<T1, T2, TResult>(out T1 obj1, out T2 obj2)
for just two parameters. We have not even touched ref. It would actually be cumbersome and confusing for developers.
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