deductionguidesforstd::multimap(3) | C++ Standard Libary | deductionguidesforstd::multimap(3) |
NAME¶
deductionguidesforstd::multimap - deductionguidesforstd::multimap
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)
multimap( InputIt, InputIt, Comp = Comp(), Alloc = Alloc() )
-> multimap<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, T>> >
(2) (since C++17)
multimap( std::initializer_list<std::pair<Key, T>>, Comp =
Comp(),
Alloc = Alloc() )
-> multimap<Key, T, Comp, Alloc>;
template< class InputIt, class Alloc >
multimap( InputIt, InputIt, Alloc ) (3) (since C++17)
-> multimap<iter_key_t<InputIt>, iter_val_t<InputIt>,
std::less<iter_key_t<InputIt>>, Alloc>;
template< class Key, class T, class Allocator >
multimap( std::initializer_list<std::pair<Key, T>>, Allocator )
(4) (since C++17)
-> multimap<Key, T, std::less<Key>, Allocator>;
where the type aliases iter_key_t, iter_val_t, iter_to_alloc_t are defined as
if as
follows
template< class InputIt >
(exposition
using iter_key_t = std::remove_const_t< only)
typename std::iterator_traits<InputIt>::value_type::first_type>;
template< class InputIt > (exposition
using iter_val_t = typename only)
std::iterator_traits<InputIt>::value_type::second_type;
template< class InputIt >
using iter_to_alloc_t = std::pair<
std::add_const_t<typename (exposition
std::iterator_traits<InputIt>::value_type::first_type>, only)
typename std::iterator_traits<InputIt>::value_type::second_type
>
This deduction guide is provided for multimap to allow deduction from an
iterator
range (overloads (1,3)) and std::initializer_list (overloads (2,4)). 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.
Example¶
// Run this code
#include <map>
int main() {
// std::multimap m1 = {{"foo", 1}, {"bar", 2}}; // Error:
braced-init-list has no type;
// cannot deduce pair<Key, T> from
// {"foo", 1} or {"bar", 2}
std::multimap m1 = {std::pair{"foo", 2}, {"bar", 3}}; //
guide #2
std::multimap 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>
2022.07.31 | http://cppreference.com |