Re: CONSTRAINT_ERROR - why?

[Jeffrey Carter <jrcarter@acm.org>]

Alfred Hilscher wrote:
> 
> Jeffrey Carter schrieb:
>>
>>declare
>>    Value : constant := X'Size / 8;
>>begin
>>    Y := Value;
>>end;
> 
> Is there no way to avoid this extra assignment? I expected something
> like function "/" (Left, Right : universal_integer) return Byte;

There is no "extra assignment". This is a static universal expression 
and is evaluated by the compiler. Value becomes a name for the resulting 
value (a "named number"). The block statement above is another way to write

Y := 33;

except that changes to X are handled automatically.

This is, however, a gotcha in Ada. The context of the expression helps 
determine the selection ("overload resolution") of the operator. Lots of 
people, including experienced people, expect the universal operation to 
be selected for an assignment to a variable or the initialization of an 
object, but that's not what the language rules say.

-- 
Jeff Carter
"C++ is like giving an AK-47 to a monk, shooting him
full of crack and letting him loose in a mall and
expecting him to balance your checking account
'when he has the time.'"
Drew Olbrich