Hello
Gesendet: Donnerstag, 14. Februar 2008 20:44
At 8:12 PM +0100 2/14/08, Jean-Pierre Bergamin wrote:
Is there a reason why boost::bind does not overload the logical operators || and &&? They definitively would come in more handy to build up complicated logical expressions than using the std::logical_and and std::logical_or function objects.
My guess is that since boost::bind could not replicate the behavior of && and ||, the authors decided not to provide them.
The built in && will not evaluate the second argument if the first is false. Similarly, the built in || will not evalulate the second argument if the first is true.
You can write if ( p != NULL && p->someField == 3 ) confident in the knowledge that "p->someField" will not be read from if p == NULL.
Thats right. But this is not really a problem of bind, but of the semantics of the function objects std::logical_and and std::logical_or itself. The second argument is always evaluated. So IMHO the programmer should be aware of that anyway when using those logical expressions. int *p_int_null = NULL; bool result = p_int_null != NULL && *p_int_null > 10; // ok logical_and<bool> and_op; result = and_op( p_int_null != NULL, *p_int_null > 10 ); // Oops Could there be a way to provide a function object safe_logical_and that only evaluates the second argument if the first one is true? Regards Jean-Pierre Bergamin