deduction guides for std::vector

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C++
Containers library
std::vector
Member types
Member functions
Non-member functions
(until C++20) (until C++20) (until C++20) (until C++20) (until C++20)
Deduction guides (C++17)
Defined in header <vector>
template < class InputIt,

class Alloc = std:: allocator <
typename std:: iterator_traits < InputIt > :: value_type > >
vector ( InputIt, InputIt, Alloc = Alloc ( ) )

- > vector < typename std:: iterator_traits < InputIt > :: value_type , Alloc > ;
(1) (since C++17)
template < ranges:: input_range R,

class Alloc = std:: allocator < ranges:: range_value_t < R >> >
vector ( std:: from_range_t , R && , Alloc = Alloc ( ) )

- > vector < ranges:: range_value_t < R > , Alloc > ;
(2) (since C++23)
1) This deduction guide is provided for vector to allow deduction from an iterator range. This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator and Alloc satisfies Allocator .
2) This deduction guide is provided for vector to allow deduction from a std::from_range_t tag and an input_range .

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 (2)

Example

Run this code 
#include <vector>
 
int main()
{
    std::vector<int> v = {1, 2, 3, 4};
 
    // uses explicit deduction guide to deduce std::vector<int>
    std::vector x(v.begin(), v.end());
 
    // deduces std::vector<std::vector<int>::iterator>
    // first phase of overload resolution for list-initialization selects the candidate
    // synthesized from the initializer-list constructor; second phase is not performed
    // and deduction guide has no effect
    std::vector y{v.begin(), v.end()};
}
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