if_contains_type.h File Reference

#include "config/policies/EmptyPolicy.h"
#include "config/type_traits/contains_type.h"

Go to the source code of this file.

Defines
#define	IF_CONTAINS_TYPE_(NAME)
	The IF_CONTAINS_TYPE_(NAME) macro generates a compile time selector class that allows for cheching on a specific subtype of type/class and enables code execution facilities in dependency of the existence of a subtype.

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Define Documentation

#define IF_CONTAINS_TYPE_

(

NAME

)

The IF_CONTAINS_TYPE_(NAME) macro generates a compile time selector class that allows for cheching on a specific subtype of type/class and enables code execution facilities in dependency of the existence of a subtype.

Parameters:

[in]

NAME

is the name of the subtype, that has to be tested.

The generated class if_contains_type_NAME supports first the type checking with the help of the macro CONTAINS_TYPE_(NAME) and second, it allows code execution in dependency of the existence of the requested type. For that purpose a compile time selector is integrated which itself is configurable with the action to support in case of existence or lack of the type. The default behaviour for else clause is do nothing, however it is up to the user to change that in a way that the user needs by providing a policy class. For an example, on how to provide a policy template class with the correct interface see ThenPolicyExample or ElsePolicyExample.

How to use it? Here is an example:

struct TypeWithTestType {
    typedef int TestType;
};

IF_CONTAINS_TYPE_(TestType);

...

// return 0, because int does not contain TestType
if_contains_type_TestType<int>::value;
// return 1, because TypeWithTestType contains TestType
if_contains_type_TestType<TypeWithTestType>:: value;

// does nothing due to the fact that int does not contain
// the type TestType and it executes nothing, because we
// have specified an empty else clause
if_contains_type_TestType<int>::ThenElse<Then>::process();

// executes the Else policy template due to the fact that
// int does not contain the type TestType
if_contains_type_TestType<int>::ThenElse<Then, Else>::process();

// executes the Then policy, because the requested type is contained
if_contains_type_TestType<TypeWithTestType>::ThenElse<Then>::process();

...

Author:

Michael Schulze