Re: how to do things like procedure foo(A: string) is bar: string := A; begin; ...;end;

[Robert Eachus <rieachus@comcast.net>]

On Monday, December 18, 2017 at 10:34:50 AM UTC-5, Mehdi Saada wrote:
 
> Not sure about the constrained formal parameter part. What happens when you call something like
> function FOO(T: String range 5..9) return String;
> with a parameter whose index subtype's bounds are say, 1..4 ? You say it would raise Constraint_Error ? If so I can see the point. There's never too much facultative checks.

Yes, the bounds don't have to match, but the lengths do. (I hope the different lengths were not a typo.)  However, there is another problem.  Way, way back subroutine parameters were changed to eliminate range constraints.  You can say:

subtype PS is String range(1..4);
subtype TS is String range(5..9);
procedure Foo(T: TS);
...
Foo(PS); --raises Constraint_Error
Foo('X' & PS); -- OK.

But:
procedure Foo(T: String range 5..9)...  -- will fail at compile time.

Why were formal parameters changed to eliminate (syntatic) constraints?  They didn't accomplish much other than to confuse users.  You can get the same effect by using explicit subtype declarations--as above--if you want it.  Making things explicit helps both reader and programmer in those cases.