是的C ++ 0x的一部分_1？ [英] Is _1 part of C++0x?

问题描述

我见过 2 最近答案使用 _1 作为一个纯粹的C ++ 0x的解决方案（升压lambda表达式没有明确提及）。

I've seen two recent answers using _1 as a pure C++0x solution (no explicit mention of boost lambdas).

有没有这样的动物如的std :: _ 1 我认为有本地lambda表达式将会使这种结构是多余的。

Is there such an animal as std::_1 I would think that having native lambdas will make such a construct redundant.

一个谷歌code搜索的std :: _ 1 带来的两个结果从同一项目的所以这是不确定的。

A Google code search for std::_1 brings two results from the same project so that's inconclusive.

推荐答案

是的，他们是C ++ 0x中的的std ::占位符命名空间内，从零件最新的草案（n3126）§20.8.10.1.3占位符：

Yes, they are part of C++0x inside the std::placeholders namespace, from the latest draft (n3126) §20.8.10.1.3 "Placeholders":

namespace std {
   namespace placeholders {
      // M is the implementation-defined number of placeholders
      extern unspecified _1;
      extern unspecified _2;
        .
        .
        .
      extern unspecified _M;
   }
}

他们实际上是 href=\"http://en.wikipedia.org/wiki/C%2B%2B_Technical_Report_1#Function_object_binders\">（的 n1836 §3.6.4;的n1455 ）与绑定，这是从的Boost.Bind库。

They are actually included in TR1 (n1836 §3.6.4; n1455) along with bind, which are taken from the Boost.Bind library.

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