deduction guides for std::vector - cppreference.com (original) (raw)

Defined in header
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)

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.

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.

[edit] Notes

Feature-test macro	Value	Std	Feature
__cpp_lib_containers_ranges	202202L	(C++23)	Ranges-aware construction and insertion; overload (2)

[edit] Example

#include int main() { std::vector v = {1, 2, 3, 4}; // uses explicit deduction guide to deduce std::vector std::vector x(v.begin(), v.end()); // deduces std::vector<std::vector::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()}; }