executor_binder::argument

The type of the function's argument.

typedef see_below argument_type;

The type of argument_type is based on the type T of the wrapper's target object:

if T is a pointer to a function type accepting a single argument, argument_type is a synonym for the return type of T;
if T is a class type with a member type argument_type, then argument_type is a synonym for T::argument_type;
otherwise argument_type is not defined.