[fpc-pascal] Feature announcement: implicit generic function specializations

[Mattias Gaertner]

On Fri, 22 Apr 2022 20:51:56 +0200
Martin Frb via fpc-pascal <fpc-pascal at lists.freepascal.org> wrote:

>[...]
> I did explore what happens if I throw different types at it, and see
> how the current implementation deals with this (what I call) lack of
> type safety.
> And also asked the question, how should it act?  (Because the current 
> behaviour is new, expected to need fixes, and can obviously be fixed).

See Sven's first mail. 

 
>[...]
> So what happens if:
> 
> var
>    b: Byte;
>    c: Cardinal;
> begin
>    Add(b, c);
> 
> Well, I tested: It uses the type of the first Param. So it calls a 
> function for both param of type Byte. The cardinal argument is 
> converted. (potentially truncated).

Yes, as explained by Sven.

 
> If you use numeric constants:
>    writeln('   0', Add(0, 0) );      // ShortInt
>    writeln('1000', Add(1000, 1000) );  // SmallInt
>    writeln('100K', Add(100000, 100000) );  // Integer
> 
> So then, if you try to fix   " Add(b, c)" by checking that b and c
> have the same type => "Add(c, 0)" will fail => because 0 is ShortInt
> and not cardinal.

Why is that a fail?

 
> ----------------------------
> I created a little test program (see bottom of mail).
> 
> And it gives a strange warning:
> 
> Compile Project, Target: 
> C:\Users\martin\AppData\Local\Temp\project1.exe: Success, Warnings:
> 1, Hints: 3
> project1.lpr(67,52) Warning: Range check error while evaluating 
> constants (100000 must be between -128 and 127)

Add(0, 100000)
Correct range error.


> project1.lpr(41,18) Hint: Local proc "Add$1" is not used
> 72 lines compiled, 0.2 sec, 105136 bytes code, 5476 bytes data
> Line 41 is the declaration of the generic
>     generic function Add<T>(aArg1, aArg2: T): T;

Maybe related to
https://gitlab.com/freepascal.org/fpc/source/-/issues/39675


>[...]

Mattias