[fpc-devel] *** GMX Spamverdacht *** Re: Dangerous optimization in CASE..OF

[Thorsten Engler]

For objects "is" compares (the type of) the value (not the type of the variable) against the specified type. Effectively telling you if you can do a hard cast of that value to that type.

For ordinals, it compares the value against the specified type. Effectively telling you if you can do a hard cast of that value to that type.

I fail to see the difference?

> -----Original Message-----
> From: fpc-devel <fpc-devel-bounces at lists.freepascal.org> On Behalf
> Of Ozz Nixon
> Sent: Saturday, 14 April 2018 22:43
> To: FPC developers' list <fpc-devel at lists.freepascal.org>
> Subject: Re: [fpc-devel] *** GMX Spamverdacht *** Re: Dangerous
> optimization in CASE..OF
> 
> I understand the thread, however, in one of the ISO standards for
> Pascal, the keyword is, is defined for type not value. The example
> I gave is the only way I can see supporting is on non objects -
> because we are a typed language. That was my point, not arguing
> against, however, sharing a way I could see a value of it. Other
> than that, I am against...
> 
> Ozz
> 
> > On Apr 14, 2018, at 8:38 AM, Thorsten Engler
> <thorsten.engler at gmx.net> wrote:
> >
> > Eh, Ozz? Did you actually read this thread?
> >
> > It has nothing to do with the declared type of i. it compares the
> current value of i against the range of the specified type and will
> return true if the current value falls inside that range.
> >
> > 5 is TSubRange -> true
> > 2000 is TSubRange -> false
> >
> > Also:
> >
> > case i as TSubRange of //exception if i < -5 or i > 5
> >
> >
> >
> >> -----Original Message-----
> >> From: fpc-devel <fpc-devel-bounces at lists.freepascal.org> On
> Behalf Of
> >> Ozz Nixon
> >> Sent: Saturday, 14 April 2018 22:13
> >> To: FPC developers' list <fpc-devel at lists.freepascal.org>
> >> Subject: *** GMX Spamverdacht *** Re: [fpc-devel] Dangerous
> >> optimization in CASE..OF
> >>
> >> I have to ask why?
> >>
> >> i is Int64 only, will always be int64 only, so all other
> comparisons
> >> are always skipped.
> >>
> >> I could see this, inside a method with an untyped parameter:
> >>
> >> procedure doSomething(myvar;out success:boolean); Begin
> >>   {… your if is comparisons …}
> >> end;
> >>
> >> This opens your method to be used for all types for param1.
> >>
> >> Ozz
> >>
> >>> On Apr 14, 2018, at 5:51 AM, Thorsten Engler
> >> <thorsten.engler at gmx.net> wrote:
> >>>
> >>> I haven't checked out the changes you made to the compiler, so
> >> you might have already covered this, but while you are at it,
> you
> >> might want to just make this work for any ordinal type with a
> well-
> >> defined upper/lower bound (any type for which High()/Low() can
> be
> >> evaluated at compile time). So:
> >>>
> >>> type
> >>> TSubRange=-5..5;
> >>> TEnum=(One, Two);
> >>>
> >>> var
> >>> i: Int64;
> >>>
> >>> begin
> >>> if i is TSubRange then
> >>>   //...
> >>> If i is TEnum then
> >>>   //...
> >>> If i is SmallInt then
> >>>   //...
> >>>
> >>> (same with "as").
> >>>
> >>>
> >>>
> >>>> -----Original Message-----
> >>>> From: fpc-devel <fpc-devel-bounces at lists.freepascal.org> On
> >> Behalf Of
> >>>> Ondrej Pokorny
> >>>> Sent: Saturday, 14 April 2018 19:03
> >>>> To: fpc-devel at lists.freepascal.org
> >>>> Subject: Re: [fpc-devel] Dangerous optimization in CASE..OF
> >>>>
> >>>> On 14.04.2018 10:39, Thorsten Engler wrote:
> >>>>> How about following the same schema as with classes?
> >>>>>
> >>>>> If 1 is TMyEnum then
> >>>>>  //use hard cast here
> >>>>
> >>>> Yes, that is reasonable as well and it will be easier to
> >> implement
> >>>> than the TryIntToEnum/IntToEnum intrinsics for me.
> >>>>
> >>>> Ondrej
> >>>> _______________________________________________
> >>>> fpc-devel maillist  -  fpc-devel at lists.freepascal.org
> >>>> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
> >>>
> >>> _______________________________________________
> >>> fpc-devel maillist  -  fpc-devel at lists.freepascal.org
> >>> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
> >>
> >> _______________________________________________
> >> fpc-devel maillist  -  fpc-devel at lists.freepascal.org
> >> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
> >
> > _______________________________________________
> > fpc-devel maillist  -  fpc-devel at lists.freepascal.org
> > http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
> 
> _______________________________________________
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