boost::trim_copy(boost::string_view()); // error

From: Olaf van der Spek (ml_at_[hidden])
Date: 2021-10-31 10:39:54

Hi,

Why does the overload for boost::string_view not work? The std one works.
Could it be made to work?

#include <boost/algorithm/string.hpp>
#include <boost/utility/string_ref.hpp>
#include <boost/utility/string_view.hpp>
#include <iostream>
#include <string_view>

int main()
{
  boost::trim_copy(boost::string_view()); // error
  boost::trim_copy(std::string_view());
}

$ g++ t0.cpp
In file included from /usr/include/boost/algorithm/string.hpp:19,
                 from t0.cpp:1:
/usr/include/boost/algorithm/string/trim.hpp: In instantiation of
‘SequenceT boost::algorithm::trim_copy_if(const SequenceT&,
PredicateT) [with SequenceT = boost::basic_string_view<char,
std::char_traits<char> >; PredicateT =
boost::algorithm::detail::is_classifiedF]’:
/usr/include/boost/algorithm/string/trim.hpp:343:49:   required from
‘SequenceT boost::algorithm::trim_copy(const SequenceT&, const
std::locale&) [with SequenceT = boost::basic_string_view<char,
std::char_traits<char> >]’
t0.cpp:10:19:   required from here
/usr/include/boost/algorithm/string/trim.hpp:319:20: error: no
matching function for call to ‘boost::basic_string_view<char,
std::char_traits<char> >::basic_string_view(const char*, const
char*&)’
  319 |             return SequenceT(
      |                    ^~~~~~~~~~
  320 |                 detail::trim_begin(
      |                 ~~~~~~~~~~~~~~~~~~~
  321 |                     ::boost::begin(Input),
      |                     ~~~~~~~~~~~~~~~~~~~~~~
  322 |                     TrimEnd,
      |                     ~~~~~~~~
  323 |                     IsSpace),
      |                     ~~~~~~~~~
  324 |                 TrimEnd
      |                 ~~~~~~~
  325 |                 );
      |                 ~
In file included from t0.cpp:3:
/usr/include/boost/utility/string_view.hpp:97:9: note: candidate:
‘template<class Allocator> boost::basic_string_view<charT,
traits>::basic_string_view(const std::__cxx11::basic_string<charT,
traits, Allocator>&) [with Allocator = Allocator; charT = char; traits
= std::char_traits<char>]’
   97 |         basic_string_view(const std::basic_string<charT,
traits, Allocator>& str) BOOST_NOEXCEPT
      |         ^~~~~~~~~~~~~~~~~
/usr/include/boost/utility/string_view.hpp:97:9: note:   template
argument deduction/substitution failed:
In file included from /usr/include/boost/algorithm/string.hpp:19,
                 from t0.cpp:1:
/usr/include/boost/algorithm/string/trim.hpp:319:20: note:
mismatched types ‘const std::__cxx11::basic_string<char,
std::char_traits<char>, Allocator>’ and ‘const char*’
  319 |             return SequenceT(
      |                    ^~~~~~~~~~
  320 |                 detail::trim_begin(
      |                 ~~~~~~~~~~~~~~~~~~~
  321 |                     ::boost::begin(Input),
      |                     ~~~~~~~~~~~~~~~~~~~~~~
  322 |                     TrimEnd,
      |                     ~~~~~~~~
  323 |                     IsSpace),
      |                     ~~~~~~~~~
  324 |                 TrimEnd
      |                 ~~~~~~~
  325 |                 );
      |                 ~
In file included from t0.cpp:3:
/usr/include/boost/utility/string_view.hpp:110:23: note: candidate:
‘constexpr boost::basic_string_view<charT,
traits>::basic_string_view(const charT*,
boost::basic_string_view<charT, traits>::size_type) [with charT =
char; traits = std::char_traits<char>; boost::basic_string_view<charT,
traits>::size_type = long unsigned int]’ (near match)
  110 |       BOOST_CONSTEXPR basic_string_view(const charT* str, size_type len)
      |                       ^~~~~~~~~~~~~~~~~
/usr/include/boost/utility/string_view.hpp:110:23: note:   conversion
of argument 2 would be ill-formed:
In file included from /usr/include/boost/algorithm/string.hpp:19,
                 from t0.cpp:1:
/usr/include/boost/algorithm/string/trim.hpp:324:17: error: invalid
conversion from
‘boost::range_detail::extract_const_iterator<boost::basic_string_view<char,
std::char_traits<char> >, true>::typ’ {aka ‘const char*’} to
‘boost::basic_string_view<char, std::char_traits<char> >::size_type’
{aka ‘long unsigned int’} [-fpermissive]
  324 |                 TrimEnd
      |                 ^~~~~~~
      |                 |
      |
boost::range_detail::extract_const_iterator<boost::basic_string_view<char,
std::char_traits<char> >, true>::type {aka const char*}
In file included from t0.cpp:3:
/usr/include/boost/utility/string_view.hpp:107:23: note: candidate:
‘constexpr boost::basic_string_view<charT,
traits>::basic_string_view(const charT*) [with charT = char; traits =
std::char_traits<char>]’
  107 |       BOOST_CONSTEXPR basic_string_view(const charT* str)
      |                       ^~~~~~~~~~~~~~~~~
/usr/include/boost/utility/string_view.hpp:107:23: note:   candidate
expects 1 argument, 2 provided
/usr/include/boost/utility/string_view.hpp:78:23: note: candidate:
‘constexpr boost::basic_string_view<charT,
traits>::basic_string_view(const boost::basic_string_view<charT,
traits>&) [with charT = char; traits = std::char_traits<char>]’
   78 |       BOOST_CONSTEXPR basic_string_view(const
basic_string_view &rhs) BOOST_NOEXCEPT
      |                       ^~~~~~~~~~~~~~~~~
/usr/include/boost/utility/string_view.hpp:78:23: note:   candidate
expects 1 argument, 2 provided
/usr/include/boost/utility/string_view.hpp:73:23: note: candidate:
‘constexpr boost::basic_string_view<charT,
traits>::basic_string_view() [with charT = char; traits =
std::char_traits<char>]’
   73 |       BOOST_CONSTEXPR basic_string_view() BOOST_NOEXCEPT
      |                       ^~~~~~~~~~~~~~~~~
/usr/include/boost/utility/string_view.hpp:73:23: note:   candidate
expects 0 arguments, 2 provided
In file included from /usr/include/boost/algorithm/string.hpp:19,
                 from t0.cpp:1:
/usr/include/boost/algorithm/string/trim.hpp: In instantiation of
‘SequenceT boost::algorithm::trim_copy_if(const SequenceT&,
PredicateT) [with SequenceT = std::basic_string_view<char>; PredicateT
= boost::algorithm::detail::is_classifiedF]’:
/usr/include/boost/algorithm/string/trim.hpp:343:49:   required from
‘SequenceT boost::algorithm::trim_copy(const SequenceT&, const
std::locale&) [with SequenceT = std::basic_string_view<char>]’
t0.cpp:11:19:   required from here
/usr/include/boost/algorithm/string/trim.hpp:324:17: error: invalid
conversion from
‘boost::range_detail::extract_const_iterator<std::basic_string_view<char>,
true>::type’ {aka ‘const char*’} to
‘std::basic_string_view<char>::size_type’ {aka ‘long unsigned int’}
[-fpermissive]
  324 |                 TrimEnd
      |                 ^~~~~~~
      |                 |
      |
boost::range_detail::extract_const_iterator<std::basic_string_view<char>,
true>::type {aka const char*}
In file included from /usr/include/c++/11/bits/basic_string.h:48,
                 from /usr/include/c++/11/string:55,
                 from
/usr/include/boost/algorithm/string/std/string_traits.hpp:15,
                 from
/usr/include/boost/algorithm/string/std_containers_traits.hpp:19,
                 from /usr/include/boost/algorithm/string.hpp:18,
                 from t0.cpp:1:
/usr/include/c++/11/string_view:137:56: note:   initializing argument
2 of ‘constexpr std::basic_string_view<_CharT,
_Traits>::basic_string_view(const _CharT*,
std::basic_string_view<_CharT, _Traits>::size_type) [with _CharT =
char; _Traits = std::char_traits<char>; std::basic_string_view<_CharT,
_Traits>::size_type = long unsigned int]’
  137 |       basic_string_view(const _CharT* __str, size_type __len) noexcept
      |                                              ~~~~~~~~~~^~~~~

-- 
Olaf