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2350. min, max, and minmax should be constexpr

Section: 27.8.9 [alg.min.max] Status: C++14 Submitter: Ville Voutilainen Opened: 2013-12-15 Last modified: 2016-01-28

Priority: 1

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Discussion:

Having min, max, and minmax constexpr was a large part of the motivation to allow reference-to-const arguments for constexpr functions as per N3039. Furthermore, initializer_lists are immutable and not-movable-from for large part in order to allow using them in constexpr contexts and other hoisting-optimizations. In N3797 version of the draft none of these functions are constexpr, and they should be made constexpr.

Proposed resolution:

This wording is relative to N3797.

1. In 27.1 [algorithms.general], header <algorithm> synopsis, and 27.8.9 [alg.min.max], change as indicated (add constexpr to every signature before min_element):

   template<class T> constexpr const T& min(const T& a, const T& b);
   template<class T, class Compare>
   constexpr const T& min(const T& a, const T& b, Compare comp);
   […]
   template<class T>
   constexpr T min(initializer_list<T> t);
   template<class T, class Compare>
   constexpr T min(initializer_list<T> t, Compare comp);
   […]
   template<class T> constexpr const T& max(const T& a, const T& b);
   template<class T, class Compare>
   constexpr const T& max(const T& a, const T& b, Compare comp);
   […]
   template<class T>
   constexpr T max(initializer_list<T> t);
   template<class T, class Compare>
   constexpr T max(initializer_list<T> t, Compare comp);
   […]
   template<class T> constexpr pair<const T&, const T&> minmax(const T& a, const T& b);
   template<class T, class Compare>
   constexpr pair<const T&, const T&> minmax(const T& a, const T& b, Compare comp);
   […]
   template<class T>
   constexpr pair<T, T> minmax(initializer_list<T> t);
   template<class T, class Compare>
   constexpr pair<T, T> minmax(initializer_list<T> t, Compare comp);