gecko-dev/mfbt/TypeTraits.h

55 lines
1.3 KiB
C++

/* This Source Code Form is subject to the terms of the Mozilla Public
* License, v. 2.0. If a copy of the MPL was not distributed with this
* file, You can obtain one at http://mozilla.org/MPL/2.0/. */
/* Template-based metaprogramming and type-testing facilities. */
#ifndef mozilla_TypeTraits_h_
#define mozilla_TypeTraits_h_
namespace mozilla {
/*
* IsBaseOf allows to know whether a given class is derived from another.
*
* Consider the following class definitions:
*
* class A {};
* class B : public A {};
* class C {};
*
* mozilla::IsBaseOf<A, B>::value is true;
* mozilla::IsBaseOf<A, C>::value is false;
*/
template<class Base, class Derived>
class IsBaseOf
{
private:
static char test(Base* b);
static int test(...);
public:
static const bool value = (sizeof(test(static_cast<Derived*>(0))) == sizeof(char));
};
/*
* Conditional selects a class between two, depending on a given boolean value.
*
* mozilla::Conditional<true, A, B>::Type is A;
* mozilla::Conditional<false, A, B>::Type is B;
*/
template<bool condition, class A, class B>
struct Conditional
{
typedef A Type;
};
template<class A, class B>
struct Conditional<false, A, B>
{
typedef B Type;
};
} /* namespace mozilla */
#endif /* mozilla_TypeTraits_h_ */