Pascal also has this, but i remember some Ada-related post from a few months ago here that had code along the lines of (imaginary syntax, i don't remember the exact code):
type Int is range 0 .. 100 check(v)
if (v = 10) or (v = 50) then error;
end;
That would allow all values of v between 0 and 100, except 10 and 50. Note that everything after (and including) "check" is something i came up (and is more Pascal-ish), not what i am talking about. I also remember that this could be used with objects so that you could have something like (this one is Object Pascal-ish, i do not know Ada):
type Foo = object
Enabled : Boolean; Magnitude : 0..1000;
check
if (Enabled and (Magnitude=0)) or
(not Enabled and (Magnitude > 0)) then error;
end;
procedure Bar;
end;
The code in check would be called whenever the object changes externally, so "Bar" can change Enabled and Magnitude with the check being invoked only at the exit of Bar to ensure object consistency and not whenever Bar does the assignment (so it can do a Enabled:=False; Magnitude:=0; and not fail at the first assignment), but assigning those values directly from outside the object would trigger it (so having a var f: Foo; and then writing f.Enabled:=True; would trigger the error).
Or at least that is what i remember understanding.
Maybe i remember some other Pascal-styled language, but the only other such language i know of is Oberon and that goes against the "put everything imaginable, plus extra more" mentality of Ada seems to have :-P.
