Functions sometimes check the sanity of the data passed to them. This could require a number of checks and error handing. For example:

Foo& Foo::operator=(const Foo& obj)
{
  if(&obj == this)
      return *this
   ...
}
 
A more convenient way of handling this situation would be to allow constraints on arguments and let the compiler check or add code to handle the condition.

For example:

Foo& Foo::operator=(const Foo& obj { &obj != this } ) <-- Argument constraint in braces
{
   ...
}
 
Possibly throwing an "argument constraint" exception for run-time evaluations and failing to compile or compiler warning for compile-time evaluations.

--Jim Smith