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2301. Why is std::tie not constexpr?

Section: 22.4.5 [tuple.creation] Status: C++14 Submitter: Rein Halbersma Opened: 2013-09-11 Last modified: 2016-01-28

Priority: 2

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Discussion:

In N3471, a bunch of routines from header <tuple> were made constexpr.

make_tuple/tuple_cat/get<>(tuple)/relational operators — all these were "constexpr-ified".

But not tie. This is similar to Issue 2275(i), where the same observation was made about forward_as_tuple.

[2014-02-13 Issaquah: Move as Immediate]

Proposed resolution:

This wording is relative to N3691.

  1. Change the header <tuple> synopsis, 22.4.1 [tuple.general] p2 as indicated:

    template<class... Types>
  constexpr tuple<Types&...> tie(Types&...) noexcept;

  2. Change 22.4.5 [tuple.creation] around p7 as indicated:

    template<class... Types>
  constexpr tuple<Types&...> tie(Types&... t) noexcept;