`const&&`绑定到所有prvalues（和xvalues）？ [英] Does `const &&` bind to all prvalues (and xvalues)?

问题描述

C ++标准定义了以下函数已删除：

The C++ standard defines the following functions deleted;

template <class T>
void ref(const T&&) = delete;

template <class T>
void cref(const T&&) = delete;

这是为了帮助确保函数不被滥用，不允许它们绑定到临时值

This is to aid in ensuring that the functions are not misused by disallowing them from binding to temporary values (rvalues).

• const&&& 绑定到所有rvalues prvalues？


• 将 const&&& 绑定到所有移动对象（xvalues;基本上从 std :: move 或类似）？

• Does const && bind to all rvalues, specifically prvalues?
• Would const && bind to all "moved objects" (xvalues; basically something returned from std::move or similar)?

• 或者相反，有些情况下，右值（prvalue或xvalue） const&&& ？
  
  
  
  
  • 如果是，如何？
  
  

  注意：从注释中有一些清楚，这个问题严重影响了经典值，即prvalue值类别。

  Note: some clarity from the comments, this question is heavily swayed to classic rvalues, the prvalue value category.

  推荐答案

  T const&& 可以绑定类型 T 或 const T 。

  strong> [dcl.init.ref] 段落5：

  From 8.5.3 [dcl.init.ref] paragraph 5:

  
  

  5 - 对类型cv1 T1的引用初始化通过类型cv2 T2的表达式如下：[...] $ $ $ b - 否则，[...]引用将是一个右值引用。 [...]
  - 如果初始化表达式
  是一个xvalue，类prvalue，数组prvalue或函数lvalue和cv1 T1是引用兼容的 cv2 T2[...]
  那么引用绑定到初始化器表达式的值[...]

  5 - A reference to type "cv1 T1" is initialized by an expression of type "cv2 T2" as follows: [...]
  — Otherwise, [...] the reference shall be an rvalue reference. [...]
  — If the initializer expression
  — is an xvalue, class prvalue, array prvalue or function lvalue and "cv1 T1" is reference-compatible with "cv2 T2" [...] then the reference is bound to the value of the initializer expression [...]

  如果初始化器表达式是非类型的prvalue，那么将创建一个用于引用绑定的临时副本（ibid）。

  If the initializer expression is a prvalue of non-class type, then a temporary copy is created for reference binding (ibid).

  引用兼容性在8.5 .3p4;它需要一个同类或基类关系和相同或更大的cv限定。

  Reference-compatibility is defined in 8.5.3p4; it requires a same-or-base-class relationship and same-or-greater cv qualification.

  所以对于一个右值绑定到 T const& ;& ，其cv-qualification必须不大于 const 。

  So for an rvalue to bind to T const&&, its cv-qualification must be no greater than const.

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