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### 3353. `locale`'s copy assignment operator should return `locale&`

Section: 28.3.1 [locale] Status: New Submitter: Stephan T. Lavavej Opened: 2019-12-06 Last modified: 2019-12-21

Priority: 3

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Discussion:

Curiously, `locale`'s copy assignment operator currently returns `const locale&`. As Casey Carter noted in microsoft/STL#268, this is:

- Weird!

- The only occurrence in the entire Standard Library.

- Preventing `locale` from satisfying `std::copyable`.

We aren't aware of any reason for this to be `const`. (I observe that this hasn't changed since N1804 on 2005-04-27 and probably goes back to C++98; I suspect that when this was originally specified, copy assignment operators were relatively new, and conventions for them weren't rigorously followed.)

[2019-12-21 Issue Prioritization]

Priority to 3 after reflector discussion based on the observation that we have implementation divergence.

Proposed resolution:

This wording is relative to N4842.

1. Modify 28.3.1 [locale] as indicated:

   >     […]
   >     ~locale(); // not virtual
   >     const locale& operator=(const locale& other) noexcept;
   >     template<class Facet> locale combine(const locale& other) const;
   >     […]

2. Modify 28.3.1.3 [locale.cons] as indicated:

   >     const locale& operator=(const locale& other) noexcept;

   > > -14- Effects: Creates a copy of `other`, replacing the current value.

   > > -15- Returns: `*this`.