[fpc-pascal] Feature announcement: Generic functions, procedures and methods

[leledumbo]

Congratulations! Nice work, Sven.
It's a bit weird to see the specialize in the middle of an expression but
that's not a problem for me. The one that needs explanation is "complex
expressions", what's the minimum requirement for an expression to be called
complex for this case?

Sven Barth-2 wrote
> Hello together!
> 
> I'm pleased to finally announce the addition of generic functions, 
> procedures and methods (collectively called "routines") to Free Pascal 
> which allows writing type safe methods that can be used for multiple
> types.
> 
> Syntax:
> 
> The syntax for declaring a generic routine is similar to declaring a 
> normal routine and also includes support for class methods:
> 
> generic [class] (procedure|function) 
> IDENTIFIER
> <TYPEARGLIST>
> [(PARAMETERLIST)][: RESULTTYPE]; MODIFIERS;
> 
> For the TYPEARGLIST the same rules apply as for generic types. Type 
> parameters declared in the TYPEARGLIST might be used in the 
> PARAMETERLIST, the RESULTTYPE and of course the body of the routine.
> 
> Generic routines can be overloaded both by TYPEARGLIST and PARAMETERLIST.
> 
> To call a generic routine you use the following syntax:
> 
> specialize IDENTIFIER
> <TYPELIST>
> [(PARAMETERS)]
> 
> For the TYPELIST the same rules apply as for specializing a generic type.
> If the routine is part of a type or variable or you're using a unit
> name to distinguish a generic routine you need to put that before the 
> "specialize":
> 
> TYPENAME.specialize IDENTIFIER
> <TYPELIST>
> [(PARAMETERS)]
> VARIABLE.specialize IDENTIFIER
> <TYPELIST>
> [(PARAMETERS)]
> UNITNAME.specialize IDENTIFIER
> <TYPELIST>
> [(PARAMETERS)]
> 
> Calls to generic routines are normal factors so they can be used as such 
> as the following example shows:
> 
> === example begin ===
> 
> {$mode objfpc}
> 
> generic function Add
> <T>
> (aLeft, aRight: T): T;
> begin
>    Result := aLeft + aRight;
> end;
> 
> begin
>    Writeln(specialize Add
> <String>
> ('Generic ', 'routines') + specialize 
> Add
> <String>
> (' with ', 'Free Pascal'));
> end.
> 
> === example end ===
> 
> Delphi compatibility:
> 
> Of course this future is also implemented in a Delphi-compatible way for 
> the Delphi modes. There the syntax for declaring a generic function is 
> like this:
> 
> [class] (procedure|function) IDENTIFIER
> <TYPELIST>
> [(PARAMETERLIST)][: 
> RETURNTYPE]; MODIFIERS;
> 
> So merely the "generic" keyword is missing. This is analogous when 
> calling a generic routine:
> 
> IDENTIFIER
> <TYPELIST>
> [(PARAMETERS)]
> 
> Because of the missing "specialize" keyword that mark specializations 
> complex expressions *do not* work in mode Delphi yet. So assignments of 
> function results are okay, but other than that you'll likely encounter 
> compiler errors.
> 
> Please note that unlike Delphi we *do* support global generic 
> functions/procedures even in Delphi mode.
> 
> Limitations/ToDos:
> 
> The feature is not yet finished and there are some limitations that yet 
> need to be overcome or parts that simply don't work yet, this includes, 
> but is not necessarily limited to:
> 
> - support for complex expressions in Delphi modes (applies to type 
> specializations as well)
> - support for pointers to generic routines (this will currently result 
> in errors at the best case and internal errors or exceptions at the worst)
> - support for the return value in modes without support for "Result"
> - support for nested generics, most importantly generic methods inside 
> generic classes
> 
> So please test and report any bugs in the bug tracker. Questions can of 
> course be asked here on the mailing list (no, this feature won't be part 
> of FPC 3.0.0).
> 
> Regards,
> Sven
> _______________________________________________
> fpc-pascal maillist  -  

> fpc-pascal at .freepascal

> http://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-pascal





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