Deduce the template parameter CHAR_TYPE from the value_type of the iterators passed to passed to the constructor of basic_string. This deduction guide does not participate unless the specified ALLOC is convertible to bsl::allocator<CHAR_TYPE>.
Declared in <bslstl_string.h>
template<
class INPUT_ITER,
class CHAR_TYPE = BloombergLP::bslstl::IteratorUtil::IterVal_t<INPUT_ITER>,
class ALLOC,
class DEFAULT_ALLOCATOR = bsl::allocator<CHAR_TYPE>>
requires bsl::is_convertible_v<ALLOC *, DEFAULT_ALLOCATOR>
basic_string<CHAR_TYPE>(
INPUT_ITER,
INPUT_ITER,
ALLOC*) -> basic_string<CHAR_TYPE>;