Removal of global placeholders causes multiple software to fail even when BOOST_BIND_GLOBAL_PLACEHOLDERS is set #458
Description
Multiple software suffered from boost global placeholders removal causing "_1 was not declared in this scope" like compiler errors. The backward compatibility was supposed to be addressed by BOOST_BIND_GLOBAL_PLACEHOLDERS, it looked like you define BOOST_BIND_GLOBAL_PLACEHOLDERS and then magically bind.hpp header is pulled in everything boost uses returning the old logic back.
But that macros is just a plug that does nothing but:
#if !defined(BOOST_BIND_GLOBAL_PLACEHOLDERS)
BOOST_PRAGMA_MESSAGE(
"The practice of declaring the Bind placeholders (_1, _2, ...) "
"in the global namespace is deprecated. Please use "
"<boost/bind/bind.hpp> + using namespace boost::placeholders, "
"or define BOOST_BIND_GLOBAL_PLACEHOLDERS to retain the current behavior."
)
#endif
defining or not defining it just affects the message, but not the logic.
When BOOST_BIND_GLOBAL_PLACEHOLDERS is defined the old logic of registering global placeholders should be back with everything using any boost header for at least 2-3 next years when all the developers patch their software.
Pulling _1 in the global scope might be the bad practice but that practice was set by boost and used widely by many developers