为什么所有的迭代器/迭代器适配器不能移动在C ++ 11？ [英] why should all iterators / iterator adaptors not-movable in C++11?
问题描述
在此问题中讨论何时在C ++ 11中使类型不可移动，我发现Scott Meyers在 comp.std.c ++ ，其中下面列出的类类型不能在C ++ 11 libeary中移动。
In this question discussed When to make a type non-movable in C++11 and I discovered Scott Meyers had similar question on comp.std.c++, where SG listed below class types are not movable in C++11 libeary.
- 所有互斥类型（recursive_mutex，timed_mutex，recursive_timed_mutex，
- condition_variable
- type_info
- error_category
- locale :: facet
- random_device
- seed_seq
- reference_wrapper
- 持续时间
- time_point
- 迭代器适配器 li>
- 所有原子类型
- once_flag
- all mutex types(recursive_mutex , timed_mutex, recursive_timed_mutex,
- condition_variable
- type_info
- error_category
- locale::facet
- random_device
- seed_seq
- reference_wrapper
- duration
- time_point
- - all iterators / iterator adaptors
- ios_base
- basic_istream::sentry
- basic_ostream::sentry
- all atomic types
- once_flag
为什么所有迭代器/迭代器适配器不可移动？
推荐答案
职位，从标准批准之前的一年，是过时的。海报是丹尼尔·克鲁格勒，一个活跃的委员会成员，它有点政治游说：
That post, from a year before the standard was ratified, is outdated. The poster is Daniel Krügler, an active committee member, and it's a bit of political lobbying:
这些是不可移动的，意外，因为用于隐式生成移动操作的
规则在匹兹堡会议上变得澄清了
。已打开常规库问题
These aren't moveable and probably some more by accident, because the rules for implicitly generated move operations became clarified just at the Pittsburgh meeting. A general library issue has been opened
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-active.html#1331
以应对图书馆中缺乏移动支持。确保你
与你的国家机构代表联系，因为我怀疑这个
问题不足以取代国家机构对FCD的评论
。
to cope for lack of move support in the library. Be sure that you contact you national body representative, because I've heart that this issue is not a sufficient replacement for a national body comment against the FCD.
换句话说，所有那些不可移动的类型都将是标准的一个showstopper bug，他希望Usenet受众中的读者要求这个问题在标准成为官方之前固定。
In other words, all those types being non-movable would be a showstopper bug for the standard, and he wants readers in the Usenet audience to demand that the problem be fixed before the standard becomes official.
缺陷已移动到已关闭列表。解决方案是为了方便起见提供链接：
The defect has been moved to the "closed" list. The resolution is (link provided for convenience):
查看规范的库部分，并添加新添加的核心功能移动特殊成员函数（ N3044 ）。
由于N3044是一个重要的资料，很容易看出为什么这样的基本功能是必不可少的。
Since N3044 is a hefty bit of material, it's easy to see why it would be essential for such basic functionality to work.
迭代器，以及任何其他具有简单的价值语义如 std :: duration 和 std :: time_point 肯定是可移动的。正如其他人所提到的，可复制性意味着可移动性，如果没有，则会破坏语言。这个职位当时没有错。而是在争论未完成的语言的破碎。
Iterators, and anything else with simple value semantics like std::duration and std::time_point, are certainly movable. As others have mentioned, copyability implies movability, and if it didn't the language would be broken. This post wasn't wrong at the time; rather it's arguing about the brokenness of the unfinished language.
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