deductionguidesforstd::map(3)

NAME
deductionguidesforstd::map - deductionguidesforstd::map

Synopsis
   Defined in header <map>
   template< class InputIt,
             class Comp = std::less<iter_key_t<InputIt>>,
             class Alloc =
   std::allocator<iter_to_alloc_t<InputIt>> > (1) (since C++17)
   map( InputIt, InputIt, Comp = Comp(), Alloc = Alloc() )
       -> map<iter_key_t<InputIt>, iter_val_t<InputIt>, Comp,
   Alloc>;
   template< class Key,
             class T,
             class Comp = std::less<Key>,
             class Alloc = std::allocator<std::pair<const Key, (2) (since C++17)
   T>> >
   map( std::initializer_list<std::pair<Key, T>>, Comp = Comp(),
   Alloc = Alloc() )
       -> map<Key, T, Comp, Alloc>;
   template< class InputIt, class Alloc >
   map( InputIt, InputIt, Alloc ) (3) (since C++17)
       -> map<iter_key_t<InputIt>, iter_val_t<InputIt>,
              std::less<iter_key_t<InputIt>>, Alloc>;
   template< class Key, class T, class Alloc >
   map( std::initializer_list<std::pair<Key, T>>, Alloc ) (4) (since C++17)
       -> map<Key, T, std::less<Key>, Alloc>;
   template< ranges::input_range R, class Compare =
   std::less<range_key_t<R>,
             class Alloc = std::allocator<range_to_alloc_t<R>> >
   map( std::from_range_t, R&&, Compare = Compare(), Alloc = (5) (since C++23)
   Alloc() )
       -> map<range_key_t<R>, range_mapped_t<R>, Compare,
   Alloc>;
   template< ranges::input_range R, class Alloc >
   map( std::from_range_t, R&&, Alloc ) (6) (since C++23)
       -> map<range_key_t<R>, range_mapped_t<R>,
   std::less<range_key_t<R>>, Alloc>;
   Exposition-only helper type aliases
   template< class InputIter >
   using iter_val_t = (exposition only*)
       typename std::iterator_traits<InputIter>::value_type;
   template< class InputIter >
   using iter_key_t = (exposition only*)
       std::remove_const_t< std::tuple_element_t<0,
   iter_val_t<InputIter>>>;
   template< class InputIter >
   using iter_mapped_t = (exposition only*)
       std::tuple_element_t<1, iter_val_t<InputIter>>;
   template< class InputIter >
   using iter_to_alloc_t =
       std::pair<std::add_const_t<tuple_element_t<0, (exposition only*)
   iter_val_t<InputIter>>>,
                 std::tuple_element_t<1,
   iter_val_t<InputIter>>>;
   template< ranges::input_range Range >
   using range_key_t = (since C++23)
                        (exposition only*)
       std::remove_const_t<typename
   ranges::range_value_t<Range>::first_type>;
   template< ranges::input_range Range >
                        (since C++23)
   using range_mapped_t = (exposition only*)
       typename ranges::range_value_t<Range>::second_type;
   template< ranges::input_range Range >
   using range_to_alloc_t =
       std::pair<std::add_const_t<typename (since C++23)
   ranges::range_value_t<Range>::first_type>, (exposition only*)
                 typename
   ranges::range_value_t<Range>::second_type>;
   1-4) These deduction guides are provided for map to allow deduction from an iterator
   range (overloads (1,3)) and std::initializer_list (overloads (2,4)).
   5,6) These deduction guides are provided for map to allow deduction from a
   std::from_range_t tag and an input_range.
   These overloads participate in overload resolution only if InputIt satisfies
   LegacyInputIterator, Alloc satisfies Allocator, and Comp does not satisfy Allocator.
   Note: the extent to which the library determines that a type does not satisfy
   LegacyInputIterator is unspecified, except that as a minimum integral types do not
   qualify as input iterators. Likewise, the extent to which it determines that a type
   does not satisfy Allocator is unspecified, except that as a minimum the member type
   Alloc::value_type must exist and the expression
   std::declval<Alloc&>().allocate(std::size_t{}) must be well-formed when treated as
   an unevaluated operand.

Notes
       Feature-test macro Value Std Feature
   __cpp_lib_containers_ranges 202202L (C++23) Ranges-aware construction and insertion;
                        overload (5,6)

Example
// Run this code
 #include <map>
 int main()
 {
     // std::map m1 = {{"foo", 1}, {"bar", 2}};
         // Error: braced-init-list has no type; cannot deduce
         // pair<Key, T> from {"foo", 1} or {"bar", 2}
     std::map m1 = {std::pair{"foo", 2}, {"bar", 3}}; // guide #2
     std::map m2(m1.begin(), m1.end()); // guide #1
 }
   Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 3025 C++17 initializer-list guides take use std::pair<Key, T>
                       std::pair<const Key, T>