iter_swap（）对swap（） - 有什么区别？ [英] iter_swap() versus swap() -- what's the difference?

问题描述

MSDN说：

swap 应优先于 iter_swap 以便向后兼容。

swap should be used in preference to iter_swap, which was included in the C++ Standard for backward compatibility.

但 comp.std.c ++说：

大多数STL算法对迭代器范围。因此，当在这些范围内交换元素时，
使用 iter_swap 是有意义的，因为这是它的
预期目的---交换指向的元素两个迭代器。这个
允许优化基于节点的序列，例如 std :: list ，其中
节点只是重新链接，而不是实际交换的数据。

Most STL algorithms operate on iterator ranges. It therefore makes sense to use iter_swap when swapping elements within those ranges, since that is its intended purpose --- swapping the elements pointed to by two iterators. This allows optimizations for node-based sequences such as std::list, whereby the nodes are just relinked, rather than the data actually being swapped.

那么哪一个是正确的呢？我应该使用 iter_swap ，还是应该使用 swap ？ （< iter_swap 仅用于向后兼容性？）为什么？

So which one is correct? Should I use iter_swap, or should I use swap? (Is iter_swap only for backwards compatibility?) Why?

推荐答案

标准本身很少提及 iter_swap ：

• 交换（* a，* b），虽然没有规定必须以这种方式实现。


• code> * a 和 * b 必须是可交换的，这意味着 * b）必须有效，因此取消引用的类型必须是相同的，但迭代器类型不必是


• 需要在 std :: reverse 的实现中使用iter_swap 。

• It should have the effect of swap(*a, *b), although there is no stipulation that it must be implemented that way.
• The dereferenced values *a and *b must be "swappable", which implies that swap(*a, *b) must be valid, and thus the dereferenced types must be identical, although the iterator types do not have to be.
• iter_swap is required to be used in the implementation of std::reverse. No such requirement is placed on any other algorithm, so this seems to be an oddity.

借用 发现的 //stackoverflow.com/a/13991936/1435577> stl / iter_swap.html> SGI文档 ：

To borrow what sehe had found from the SGI docs:

严格地说， iter_swap 是多余的。它只存在于技术原因：在某些情况下，一些编译器难以执行解释 swap（* a，* b）所需的类型扣除。

Strictly speaking, iter_swap is redundant. It exists only for technical reasons: in some circumstances, some compilers have difficulty performing the type deduction required to interpret swap(*a, *b).

所有这些似乎暗示它是过去的神器。

All of these seem to suggest that it is an artifact of the past.

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