std::ranges::max
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Constrained algorithms
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std::ranges
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Defined in header
<algorithm>
Call signature
template< class T, class Proj = std::identity,
(1)
(since C++20)
std::indirect_strict_weak_order <
std::projected <const T*, Proj>> Comp = ranges::less >
constexpr const T&
template< std::copyable T, class Proj = std::identity,
(2)
(since C++20)
std::indirect_strict_weak_order <
std::projected <const T*, Proj>> Comp = ranges::less >
constexpr T
template< ranges::input_range R, class Proj = std::identity,
(3)
(since C++20)
std::indirect_strict_weak_order <
std::projected <ranges::iterator_t <R>, Proj>> Comp = ranges::less >
requires std::indirectly_copyable_storable <ranges::iterator_t <R>,
ranges::range_value_t <R>*>
constexpr ranges::range_value_t <R>
Returns the greater of the given projected values.
1) Returns the greater of a and b.
2) Returns the first greatest value in the initializer list r.
3) Returns the first greatest value in the range r.
The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:
- Explicit template argument lists cannot be specified when calling any of them.
- None of them are visible to argument-dependent lookup.
- When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.
Contents
[edit] Parameters
a, b
-
the values to compare
r
-
the range of values to compare
comp
-
comparison to apply to the projected elements
proj
-
projection to apply to the elements
[edit] Return value
1) The greater of a and b, according to their respective projected values. If they are equivalent, returns a.
2,3) The greatest value in r, according to the projection. If several values are equivalent to the greatest, returns the leftmost one. If the range is empty (as determined by ranges::distance (r)), the behavior is undefined.
[edit] Complexity
1) Exactly one comparison.
2,3) Exactly ranges::distance (r) - 1 comparisons.
[edit] Possible implementation
struct max_fn { template<class T, class Proj = std::identity, std::indirect_strict_weak_order < std::projected <const T*, Proj>> Comp = ranges::less > constexpr const T& operator()(const T& a, const T& b, Comp comp = {}, Proj proj = {}) const { return std::invoke (comp, std::invoke (proj, a), std::invoke (proj, b)) ? b : a; } template<std::copyable T, class Proj = std::identity, std::indirect_strict_weak_order < std::projected <const T*, Proj>> Comp = ranges::less > constexpr T operator()(std::initializer_list <T> r, Comp comp = {}, Proj proj = {}) const { return *ranges::max_element (r, std::ref (comp), std::ref (proj)); } template<ranges::input_range R, class Proj = std::identity, std::indirect_strict_weak_order < std::projected <ranges::iterator_t <R>, Proj>> Comp = ranges::less > requires std::indirectly_copyable_storable <ranges::iterator_t <R>, ranges::range_value_t <R>*> constexpr ranges::range_value_t <R> operator()(R&& r, Comp comp = {}, Proj proj = {}) const { using V = ranges::range_value_t <R>; if constexpr (ranges::forward_range <R>) return static_cast<V>(*ranges::max_element (r, std::ref (comp), std::ref (proj))); else { auto i = ranges::begin (r); auto s = ranges::end (r); V m(*i); while (++i != s) if (std::invoke (comp, std::invoke (proj, m), std::invoke (proj, *i))) m = *i; return m; } } }; inline constexpr max_fn max;
[edit] Notes
Capturing the result of std::ranges::max by reference produces a dangling reference if one of the parameters is a temporary and that parameter is returned:
int n = -1; const int& r = std::ranges::max(n + 2, n * 2); // r is dangling
[edit] Example
Run this code
#include <algorithm> #include <iostream> #include <string> static_assert(std::ranges::max({0B10, 0X10, 010, 10}) == 16); // overload (2) int main() { namespace ranges = std::ranges; using namespace std::string_view_literals; std::cout << "larger of 1 and 9999: " << ranges::max(1, 9999) << '\n' << "larger of 'a', and 'b': '" << ranges::max('a', 'b') << "'\n" << "longest of \"foo\", \"bar\", and \"hello\": \"" << ranges::max({"foo"sv, "bar"sv, "hello"sv}, {}, &std::string_view::size) << "\"\n"; }
Output:
larger of 1 and 9999: 9999 larger of 'a', and 'b': 'b' longest of "foo", "bar", and "hello": "hello"