On 22.04.2018 10:46, Luca Olivetti wrote:
El 22/04/18 a les 06:53, Ondrej Pokorny ha escrit:
My goal is to get the best from it. If disallowing of IS/AS for enums
with holes in FPC modes is a requirement for applying the patch, I am
OK with this sacrifice.
Why disallow it instead of simply checking if it's one of the valid
values?
What do you understand with "valid values"? Do you mean "declared values"?
Reasons why I haven't worked on checking declared values in assigned enums:
1.) It's not "simply checking". The check would be much more complex
than a simple low-high check. At least I cannot do that for an arbitrary
assigned enum - I admit I don't have enough compiler knowledge and
motivation. I don't use assigned enums myself.
2.) I am not even 100% sure what valid values are in assigned enums. At
least no FPC developer has confirmed yet what they understand with valid
values for assigned enums. I assume only "declared values" are "valid
values" (unlike in Delphi where the whole range is valid) but nobody
from FPC team has confirmed it yet (or I missed it).
3.) It is potentially very dangerous if the IS/AS operator behaved
differently in Delphi and FPC mode. I feel that modes are more about
syntax sugar and not about substantially different behavior. The clean
way to go is to write a compiler intrinsic that checks for declared
values only (in all modes) and a different intrinsic to check for valid
range (in all modes) and make the IS/AS operator to duplicate one of
these intrinsics on all modes, eventually disabling it in some modes for
unclear preconditions.
+++
So: if Sven (or the FPC team) think that the IS/AS check for valid range
of assigned enums doesn't belong to FPC mode, it's better to disallow it
there and not change its behavior.
+++
And as always: feel free to extend the patch and add support for
checking only declared values in assigned enums - if you have the skill
and motivation and you believe it can and will be applied to FPC trunk.
(I write this without any offense.)
Ondrej
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