Generic functions (C++/CLI)
A generic function is a function that is declared with type parameters. When called, actual types are used instead of the type parameters.
This feature doesn't apply to all platforms.
This feature isn't supported in the Windows Runtime.
Not applicable.
A generic function is a function that's declared with generic type parameters. When called, actual types are used instead of the type parameters.
generic-declaration
:
generic
<
generic-parameter-list
>
constraint-clause-list
opt function-definition
generic-parameter-list
:
generic-parameter
generic-parameter-list
,
generic-parameter
generic-parameter
:
attributes
opt class
identifier
attributes
opt typename
identifier
constraint-clause-list
:
constraint-clause-list
opt constraint-clause
constraint-clause
:
where
identifier
:
constraint-item-list
constraint-item-list
:
constraint-item
constraint-item-list
,
constraint-item
constraint-item
:
type-id
ref class
ref struct
value class
value struct
gcnew ( )
generic-id
:
generic-name
<
generic-argument-list
>
generic-name
:
identifier
operator-function-id
generic-argument-list
:
generic-argument
generic-argument-list
,
generic-argument
generic-argument
:
type-id
generic-parameter-list
A comma-separated list of optionally attributed generic type parameter identifiers.
attributes
(Optional) Extra declarative information. For more information on attributes and attribute classes, see attributes.
constraint-clause-list
This optional list specifies restrictions on the types that may be used as type arguments. It takes the form specified in Constraints on generic type parameters (C++/CLI).
function-definition
A definition of a method or standalone function. The function may not have a virtual
modifier, which isn't allowed since virtual methods may not be generic. The body of the function may refer to the generic type parameter identifiers. The function may be an operator
function.
generic-id
When you invoke an instance of a generic function, you specify the types used to implement it in the generic-argument-list
. This list corresponds to the generic-parameter-list
, and must satisfy the constraints of the optional constraint-clause-list
.
generic-name
A generic function may have an identifier
as its name, or it may be an operator
function.
Generic functions are functions declared with one or more generic type parameters. They may be methods in a class
or struct
, or standalone functions. A single generic declaration implicitly declares a family of functions that differ only in the substitution of a different actual type for the generic type parameter.
A class
or struct
constructor may not be declared with generic type parameters.
When called, the generic type parameter is replaced by an actual type. The actual type may be explicitly specified in angled brackets using syntax similar to a function template call. If called without the type parameters, the compiler will attempt to deduce the actual type from the parameters supplied in the function call. The compiler reports an error if the intended type argument can't be deduced from the parameters used.
Compiler option: /clr
The following code sample demonstrates a generic function.
// generics_generic_function_1.cpp
// compile with: /clr
generic <typename ItemType>
void G(int i) {}
ref struct A {
generic <typename ItemType>
void G(ItemType) {}
generic <typename ItemType>
static void H(int i) {}
};
int main() {
A myObject;
// generic function call
myObject.G<int>(10);
// generic function call with type parameters deduced
myObject.G(10);
// static generic function call
A::H<int>(10);
// global generic function call
G<int>(10);
}
Generic functions can be overloaded based on signature or arity, the number of type parameters on a function. Also, generic functions can be overloaded with non-generic functions of the same name, as long as the functions differ in some type parameters. For example, the following functions can be overloaded:
// generics_generic_function_2.cpp
// compile with: /clr /c
ref struct MyClass {
void MyMythod(int i) {}
generic <class T>
void MyMythod(int i) {}
generic <class T, class V>
void MyMythod(int i) {}
};
The following example uses a generic function to find the first element in an array. It declares MyClass
, which inherits from the base class MyBaseClass
. MyClass
contains a generic function, MyFunction
, which calls another generic function, MyBaseClassFunction
, within the base class. In main
, the generic function, MyFunction
, is called using different type arguments.
// generics_generic_function_3.cpp
// compile with: /clr
using namespace System;
ref class MyBaseClass {
protected:
generic <class ItemType>
ItemType MyBaseClassFunction(ItemType item) {
return item;
}
};
ref class MyClass: public MyBaseClass {
public:
generic <class ItemType>
ItemType MyFunction(ItemType item) {
return MyBaseClass::MyBaseClassFunction<ItemType>(item);
}
};
int main() {
MyClass^ myObj = gcnew MyClass();
// Call MyFunction using an int.
Console::WriteLine("My function returned an int: {0}",
myObj->MyFunction<int>(2003));
// Call MyFunction using a string.
Console::WriteLine("My function returned a string: {0}",
myObj->MyFunction<String^>("Hello generic functions!"));
}
My function returned an int: 2003
My function returned a string: Hello generic functions!