What exaxctly does boost::bind do ??

[John E]

What does boost:bind do? I've never really thought about it before (I simply took it for granted) but apparently, this statement is perfectly valid code...

boost::bind(some_function_name);

but what exactly does it do

[superbonzo]

as far as I know, the main reason is to allow composition with nullary functions:

int foo();
void bar( int c );

int main() {
  bar( foo() ); // this is the expression we want to bind
  bind( bar, foo )(); // this won't compile, as if calling bar(foo);
  bind( bar, foo() )(); // this works, but it's not what we really want ( foo is invoked once at bind time )
  bind( bar, bind(foo) )(); // this works: bind turns foo into a nullary bind expression, informing the outer bind that a composition is requested
}