[fpc-devel] if-then-else expression

[Sven Barth]

Hairy Pixels via fpc-devel <fpc-devel at lists.freepascal.org> schrieb am Do.,
28. Aug. 2025, 09:55:

> On Aug 26, 2025 at 3:49:43 AM, Nikolay Nikolov via fpc-devel <
> fpc-devel at lists.freepascal.org> wrote:
>
>> But they're not 100% compatible, are they? IfThen evaluates both the true
>> and the false parameter, while the 'if' statement doesn't. For example:
>>
>> s := IfThen(b <> 0, a div b, 999)
>>
>> Will raise a division by zero exception, if b is 0, while
>>
>> s := if b <> 0 then a div b else 999
>>
>> won't.
>>
>> Nikolay
>>
>
> I think if the call was inlined it wouldn’t but otherwise it would. FPC
> can’t reliably inline either so you wouldn’t want to risk that.
>

That's wrong. Inlining does *not* change side effects (and if it does that
is considered a bug), so parameters are evaluated before the inlined
function's code is executed.


If that’s a concern then IfThen could be an intrinsic. It’s basically just
> a macro to a if statement with an assignment. Extremely simple thing to
> implement.
>

There had already been an IfThen-intrinisic almost ten years ago, which was
then rejected and reverted cause due to its different behavior to a
ordinary function would lead to more confusion.

The if-the-expression is just as easy to implement and is now required for
Delphi compatibility anyway, so there will not be any discussion about this
anymore.

Regards,
Sven

>
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