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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@78848 91177308-0d34-0410-b5e6-96231b3b80d8
82 lines
3.0 KiB
C++
82 lines
3.0 KiB
C++
//===- llvm/Support/type_traits.h - Simplfied type traits -------*- C++ -*-===//
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//
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// The LLVM Compiler Infrastructure
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//
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// This file is distributed under the University of Illinois Open Source
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// License. See LICENSE.TXT for details.
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//
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//===----------------------------------------------------------------------===//
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//
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// This file provides a template class that determines if a type is a class or
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// not. The basic mechanism, based on using the pointer to member function of
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// a zero argument to a function was "boosted" from the boost type_traits
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// library. See http://www.boost.org/ for all the gory details.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_SUPPORT_TYPE_TRAITS_H
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#define LLVM_SUPPORT_TYPE_TRAITS_H
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// This is actually the conforming implementation which works with abstract
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// classes. However, enough compilers have trouble with it that most will use
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// the one in boost/type_traits/object_traits.hpp. This implementation actually
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// works with VC7.0, but other interactions seem to fail when we use it.
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namespace llvm {
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namespace dont_use
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{
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// These two functions should never be used. They are helpers to
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// the is_class template below. They cannot be located inside
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// is_class because doing so causes at least GCC to think that
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// the value of the "value" enumerator is not constant. Placing
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// them out here (for some strange reason) allows the sizeof
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// operator against them to magically be constant. This is
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// important to make the is_class<T>::value idiom zero cost. it
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// evaluates to a constant 1 or 0 depending on whether the
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// parameter T is a class or not (respectively).
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template<typename T> char is_class_helper(void(T::*)());
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template<typename T> double is_class_helper(...);
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}
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template <typename T>
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struct is_class
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{
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// is_class<> metafunction due to Paul Mensonides (leavings@attbi.com). For
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// more details:
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// http://groups.google.com/groups?hl=en&selm=000001c1cc83%24e154d5e0%247772e50c%40c161550a&rnum=1
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public:
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enum { value = sizeof(char) == sizeof(dont_use::is_class_helper<T>(0)) };
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};
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// enable_if_c - Enable/disable a template based on a metafunction
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template<bool Cond, typename T = void>
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struct enable_if_c {
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typedef T type;
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};
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template<typename T> struct enable_if_c<false, T> { };
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// enable_if - Enable/disable a template based on a metafunction
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template<typename Cond, typename T = void>
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struct enable_if : public enable_if_c<Cond::value, T> { };
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namespace dont_use {
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template<typename Base> char base_of_helper(const volatile Base*);
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template<typename Base> double base_of_helper(...);
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}
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/// is_base_of - Metafunction to determine whether one type is a base class of
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/// (or identical to) another type.
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template<typename Base, typename Derived>
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struct is_base_of {
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static const bool value
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= is_class<Base>::value && is_class<Derived>::value &&
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sizeof(char) == sizeof(dont_use::base_of_helper<Base>((Derived*)0));
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};
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}
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#endif
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