id	summary	reporter	owner	description	type	status	milestone	component	version	severity	resolution	keywords	cc
11570	Boost 1.59.0 breaks lexical_cast to a move-only type (from a string)	Tony Lewis <tonyelewis@…>	Antony Polukhin	"I think lexical_cast 1.59.0 introduces a regression over 1.58.0 because 1.58.0 allows lexical_cast from string to a move-only type but this now fails to compile.

C++11 example:

{{{
#!cpp
#include <boost/lexical_cast.hpp>

#include <iostream>
#include <string>

using boost::lexical_cast;

using namespace std;

struct my_move_only final {
	string data;

	my_move_only() = default;
	my_move_only(my_move_only &&) = default;
	my_move_only(const my_move_only &) = delete;
};

istream & operator>>(istream &arg_is, my_move_only &arg_mot) {
	arg_is >> arg_mot.data;
	return arg_is;
}

int main() {
	cerr << ""from string gives : "" << lexical_cast<my_move_only>( string{ ""mr_carbohdrate"" } ).data << endl;
}
}}}

This works against Boost 1.58.0 under both `g++ -std=c++11` and `clang++ -std=c++11 -stdlib=libc++` but fails against Boost 1.59.0 under both.

The key compile error message appears to be:

{{{
boost/lexical_cast.hpp:46:26: error: use of deleted function ‘my_move_only::my_move_only(const my_move_only&)’
         return get(result);
}}}

(ie, you're trying to copy-construct this move-only type).

It looks to me like this functionality broke with commit [https://github.com/boostorg/lexical_cast/commit/bdc355759e3259209f1107ae21babee6dcf8d80b bdc355759e].

Is it possible to keep that commit's benefits whilst restoring support for move-only types? Perhaps with some `std::move()` magic?"	Bugs	closed	Boost 1.60.0	lexical_cast	Boost 1.59.0	Regression	fixed	lexical_cast,move-only,1.59.0,copy constructor,regression