CHAPTER 19 GENERICS

Generic Delegates

Generic delegates are very much like nongeneric delegates, except that the type parameters determine the characteristics of what methods will be accepted.

•To declare a generic delegate, place the type parameter list in angle brackets after the delegate name and before the delegate parameter list.

Type parameters

↓

delegate R MyDelegate<T, R>( T value );

•Notice that there are two parameter lists: the delegate formal parameter list and the type parameter list.

•The scope of the type parameters includes the following:

—The return type

—The formal parameter list

—The constraint clauses

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CHAPTER 19 GENERICS

The following code shows an example of a generic delegate. In Main, generic delegate MyDelegate is instantiated with an argument of type string and initialized with method PrintString.

}

}

This code produces the following output:

Hi There.

HI THERE.

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CHAPTER 19 GENERICS

Another Generic Delegate Example

Since the LINQ feature of C# 3.0 uses generic delegates extensively, it’s worth showing another example before we get there. I’ll cover LINQ itself, and more about its generic delegates, in Chapter 21.

The following code declares a generic delegate named Func, which takes methods with two parameters and that return a value. The method return type is represented as TR, and the method parameter types are represented as T1 and T2.

Delegate parameter type

↓ ↓ ↓ ↓

public delegate TR Func<T1, T2, TR>(T1 p1, T2 p2); // Generic delegate

static public string PrintString(int p1, int p2) // Method matches delegate

{

int total = p1 + p2; return total.ToString();

}

new Func<int, int, string>(Simple.PrintString);

Console.WriteLine("Total: {0}", myDel(15, 13)); // Call delegate

}

}

This code produces the following output:

Total: 28

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