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### 3362. Strike `stop_source`'s `operator!=`

Section: 33.3.4 [stopsource] Status: C++20 Submitter: Tim Song Opened: 2020-01-03 Last modified: 2021-02-25

Priority: 0

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Discussion:

Just like `stop_token` (see LWG 3254), `stop_source` in 33.3.4 [stopsource] declares an `operator!=` friend that is unnecessary in light of the new core language rules and should be struck.

[2020-01-14 Status set to Tentatively Ready after six positive votes on the reflector.]

Proposed resolution:

This wording is relative to N4842.

1. Modify 33.3.4 [stopsource], class `stop_source` synopsis, as indicated:

   >     namespace std {
   >       […]

   >       class stop_source {
   >       public:
   >         […]

   >         [[nodiscard]] friend bool
   >         operator==(const stop_source& lhs, const stop_source& rhs) noexcept;
   >         [[nodiscard]] friend bool
   >         operator!=(const stop_source& lhs, const stop_source& rhs) noexcept;
   >         friend void swap(stop_source& lhs, stop_source& rhs) noexcept;
   >       };
   >     }

2. Modify [stopsource.cmp] and [stopsource.special] as indicated:

   > 32.3.4.3 Non-member functions Comparisons [stopsource.nonmembers cmp]

   >     [[nodiscard]] bool operator==(const stop_source& lhs, const stop_source& rhs) noexcept;

   > > -1- Returns: `true` if `lhs` and `rhs` have ownership of the same stop state or if both `lhs` and `rhs` do not have ownership of a stop state; otherwise `false`.

   >     [[nodiscard]] bool operator!=(const stop_source& lhs, const stop_source& rhs) noexcept;

   > > -2- Returns: `!(lhs==rhs)`.

   > 32.3.4.4 Specialized algorithms [stopsource.special]

   >     friend void swap(stop_source& x, stop_source& y) noexcept;

   > > -1- Effects: Equivalent to: `x.swap(y)`.