Generic Delegates (C++)
You can use generic type parameters with delegates. For more information on delegates, see delegate.
[attributes]
generic < [class | typename] type-parameter-identifiers >
[type-parameter-constraints-clauses]
[accessibility-modifiers] delegate result-type identifier
([formal-parameters]);
Parameters
- attributes (Optional)
Additional declarative information. For more information on attributes and attribute classes, see Attributes.
- type-parameter-identifier(s)
Comma-separated list of identifiers for the type parameters.
- type-parameter-constraints-clauses
Takes the form specified in Constraints
- accessibility-modifiers (Optional)
Accessibility modifiers (e.g. public, private).
- result-type
The return type of the delegate.
- identifier
The name of the delegate.
- formal-parameters (Optional)
The parameter list of the delegate.
Example
The delegate type parameters are specified at the point where a delegate object is created. Both the delegate and method associated with it must have the same signature. The following is an example of a generic delegate declaration.
// generics_generic_delegate1.cpp
// compile with: /clr /c
generic < class ItemType>
delegate ItemType GenDelegate(ItemType p1, ItemType% p2);
The following sample shows that
You cannot use the same delegate object with different constructed types. Create different delegate objects for different types.
A generic delegate can be associated with a generic method.
When a generic method is called without specifying type arguments, the compiler tries to infer the type arguments for the call.
// generics_generic_delegate2.cpp
// compile with: /clr
generic < class ItemType>
delegate ItemType GenDelegate(ItemType p1, ItemType% p2);
generic < class ItemType>
ref struct MyGenClass {
ItemType MyMethod(ItemType i, ItemType % j) {
return ItemType();
}
};
ref struct MyClass {
generic < class ItemType>
static ItemType MyStaticMethod(ItemType i, ItemType % j) {
return ItemType();
}
};
int main() {
MyGenClass<int> ^ myObj1 = gcnew MyGenClass<int>();
MyGenClass<double> ^ myObj2 = gcnew MyGenClass<double>();
GenDelegate<int>^ myDelegate1 =
gcnew GenDelegate<int>(myObj1, &MyGenClass<int>::MyMethod);
GenDelegate<double>^ myDelegate2 =
gcnew GenDelegate<double>(myObj2, &MyGenClass<double>::MyMethod);
GenDelegate<int>^ myDelegate =
gcnew GenDelegate<int>(&MyClass::MyStaticMethod<int>);
}
The following example declares a generic delegate GenDelegate<ItemType>, and then instantiates it by associating it to the method MyMethod that uses the type parameter ItemType. Two instances of the delegate (an integer and a double) are created and invoked.
// generics_generic_delegate.cpp
// compile with: /clr
using namespace System;
// declare generic delegate
generic <typename ItemType>
delegate ItemType GenDelegate (ItemType p1, ItemType% p2);
// Declare a generic class:
generic <typename ItemType>
ref class MyGenClass {
public:
ItemType MyMethod(ItemType p1, ItemType% p2) {
p2 = p1;
return p1;
}
};
int main() {
int i = 0, j = 0;
double m = 0.0, n = 0.0;
MyGenClass<int>^ myObj1 = gcnew MyGenClass<int>();
MyGenClass<double>^ myObj2 = gcnew MyGenClass<double>();
// Instantiate a delegate using int.
GenDelegate<int>^ MyDelegate1 =
gcnew GenDelegate<int>(myObj1, &MyGenClass<int>::MyMethod);
// Invoke the integer delegate using MyMethod.
i = MyDelegate1(123, j);
Console::WriteLine(
"Invoking the integer delegate: i = {0}, j = {1}", i, j);
// Instantiate a delegate using double.
GenDelegate<double>^ MyDelegate2 =
gcnew GenDelegate<double>(myObj2, &MyGenClass<double>::MyMethod);
// Invoke the integer delegate using MyMethod.
m = MyDelegate2(0.123, n);
Console::WriteLine(
"Invoking the double delegate: m = {0}, n = {1}", m, n);
}
Output
Invoking the integer delegate: i = 123, j = 123 Invoking the double delegate: m = 0.123, n = 0.123