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### 3374. P0653 + P1006 should have made the other `std::to_address` overload `constexpr`

Section: 20.2.4 [pointer.conversion] Status: C++20 Submitter: Billy O'Neal III Opened: 2020-01-14 Last modified: 2021-02-25

Priority: 0

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Discussion:

While reviewing some interactions with P0653 + P1006, Billy discovered that one of the overloads was missing the `constexpr` tag. This might be a typo or a missed merge interaction between P0653 (which adds `to_address` with the pointer overload being `constexpr`) and P1006 (which makes `pointer_traits::pointer_to constexpr`). Mail was sent the LWG reflector, and Glen Fernandes, the author of P0653, indicates that this might have been an oversight.

[2020-02-01 Status set to Tentatively Ready after seven positive votes on the reflector.]

Proposed resolution:

This wording is relative to N4842.

1. Modify 20.2.2 [memory.syn], header `<memory>` synopsis, as indicated:

   >     […]
   >     // 20.2.4 [pointer.conversion], pointer conversion
   >     template<class T>
   >       constexpr T* to_address(T* p) noexcept;
   >     template<class Ptr>
   >       constexpr auto to_address(const Ptr& p) noexcept;
   >     […]

2. Modify 20.2.4 [pointer.conversion] as indicated:

   >     template<class Ptr> constexpr auto to_address(const Ptr& p) noexcept;

   > > -3- Returns: `pointer_traits<Ptr>::to_address(p)` if that expression is well-formed (see 20.2.3.4 [pointer.traits.optmem]), otherwise `to_address(p.operator->())`.