stl_construct.h

/*
 *
 * Copyright (c) 1994
 * Hewlett-Packard Company
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Hewlett-Packard Company makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 *
 *
 * Copyright (c) 1996,1997
 * Silicon Graphics Computer Systems, Inc.
 *
 * Permission to use, copy, modify, distribute and sell this software
 * and its documentation for any purpose is hereby granted without fee,
 * provided that the above copyright notice appear in all copies and
 * that both that copyright notice and this permission notice appear
 * in supporting documentation.  Silicon Graphics makes no
 * representations about the suitability of this software for any
 * purpose.  It is provided "as is" without express or implied warranty.
 */

/* NOTE: This is an internal header file, included by other STL headers.
 *   You should not attempt to use it directly.
 */

#ifndef __SGI_STL_INTERNAL_CONSTRUCT_H
#define __SGI_STL_INTERNAL_CONSTRUCT_H

#include <new.h>	//欲使用placement new，需要先包含此文件

__STL_BEGIN_NAMESPACE

template <class T1, class T2>
inline void construct(T1* p, const T2& value) {
  new (p) T1(value);//placement new，调用T1::T1(value);
}

//destory()第一个版本，接受一个指针
template <class T>
inline void destroy(T* pointer) {
    pointer->~T();
}

//如果元素的类型有non-trivail destructor
template <class ForwardIterator>
inline void
__destroy_aux(ForwardIterator first, ForwardIterator last, __false_type) {
  for ( ; first < last; ++first)
    destroy(&*first);//为每一元素调用第一个版本的destory()
}

//如果元素的类型有trivail destructor
template <class ForwardIterator> 
inline void __destroy_aux(ForwardIterator, ForwardIterator, __true_type) {}

//判断元素的类型是否有trivial destructor
//如果first和last区间很大，而元素的类型有trivail destructor，那么遍历会增加开销，
//因此，如果元素的类型有trivail destructor，那么什么事也不做
template <class ForwardIterator, class T>
inline void __destroy(ForwardIterator first, ForwardIterator last, T*) {
  typedef typename __type_traits<T>::has_trivial_destructor trivial_destructor;
  __destroy_aux(first, last, trivial_destructor());
}

//destory()第二个版本，接受两个迭代器，此函数设法找出元素的类型
//进而利用__type_traits<> 求取最适当的措施template <class ForwardIterator>
inline void destroy(ForwardIterator first, ForwardIterator last) {
  __destroy(first, last, value_type(first));
}

//destory()第二个版本针对迭代器为char*和wchar_t*的特化版本
inline void destroy(char*, char*) {}
inline void destroy(wchar_t*, wchar_t*) {}

__STL_END_NAMESPACE

#endif /* __SGI_STL_INTERNAL_CONSTRUCT_H */

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