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deduction guides for std::basic_string

From cppreference.com
< cpp‎ | string‎ | basic string
 
C++
 
Strings library
 
std::basic_string
 
Defined in header <string>
template< class InputIt,

          class Alloc = std::allocator<typename std::iterator_traits
                                                    <InputIt>::value_type> >
basic_string( InputIt, InputIt, Alloc = Alloc() )
    -> basic_string<typename std::iterator_traits<InputIt>::value_type,
                    std::char_traits
                        <typename std::iterator_traits<InputIt>::value_type>,

                         Alloc>;
 (1) (since C++17)
template< class CharT,

          class Traits,
          class Alloc = std::allocator<CharT> >
explicit basic_string( std::basic_string_view<CharT, Traits>,
                       const Alloc& = Alloc() )

    -> basic_string<CharT, Traits, Alloc>;
 (2) (since C++17)
template< class CharT,

          class Traits,
          class Alloc = std::allocator<CharT> >
basic_string( std::basic_string_view<CharT, Traits>,
              typename /* see below */::size_type,
              typename /* see below */::size_type,
              const Alloc& = Alloc() )

    -> basic_string<CharT, Traits, Alloc>;
 (3) (since C++17)
template< ranges::input_range R,

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

                    std::char_traits<ranges::range_value_t<R>>, Alloc>;
 (4) (since C++23)
1) This deduction guide is provided for std::basic_string to allow deduction from an iterator range. This overload participates in overload resolution only if InputIt satisfies LegacyInputIterator and Alloc satisfies Allocator.
2,3) These deduction guides are provided for std::basic_string to allow deduction from a std::basic_string_view. These overloads participate in overload resolution only if Alloc satisfies Allocator.
3) The size_type parameter type refers to the nested type size_type of the type deduced by the deduction guide.
4) This deduction guide is provided for std::basic_string 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.

Contents

[edit] Notes

Guides (2,3) are needed because the std::basic_string constructors for std::basic_string_views are made templates to avoid causing ambiguities in existing code, and those templates do not support class template argument deduction.

[edit] Notes

Feature-test macro Value Std Feature