> On Nov 6, 2018, at 11:19 PM, Sven Barth via fpc-pascal
> <fpc-pascal@lists.freepascal.org> wrote:
>
> Complex inline specializations containing, for example a multiplication with
> specializations on the left and the right side are currently not possible in
> mode Delphi. In addition to that Delphi allows overloads of generic types
> with variables and constants, so when the parser encounters "Bla<N" and has
> not yet encountered the ">" it does not know whether it needs to start a
> specialization or an expression. This is already annoying enough to solve
> with merely types, but if the right side of the "<" can also take constants
> for generics that gets downright proplematic.
Can you show full a code example? If it really is so problematic because of
something Delphi does then maybe it’s best left to objfpc mode until it can be
resolved.
> Specialization is an expensive operation. When the compiler can already
> decide that "Something<SomeType, SomeOtherType>" can never be valid, because
> it's declared as "Something<T, const N>", then this is preferable. Otherwise
> the user might get some cryptic error message during the specialization,
> because "SomeOtherType" is used where only a constant can be used.
> Pascal is considered a type safe language and without forcing users to
> decorate such parameters as "const" you essentially allow users to mix types
> and constants.
> Not to mention that parsing the generic can already be done more correctly
> then it could be if the parameter is a typesym (which it would be right now).
> You can't do e.g. "const SomeOtherConst = ConstParam * Pi" that way as it
> would mean to ease up the compiler's restrictions for type checking even
> more.
I guess if you include const it could save some compile time if you tried to
specialize with the wrong type? It’s a pretty minor savings but that’s ok.
type
generic TList<T,const U> = record
list: array[0..U-1] of T;
function capacity: integer;
end;
Btw I only implemented this with integers (no strings or floats) because afaik
this feature is only useful for arrays. I guess you could use non-ints for
default parameters but this is probably a stupid idea because of how much
compile time you’ll add to specialize a large amount of types.
Is there any reason to support strings and floats?
type
generic TCaller<T,const U> = record
procedure Say(message:T = U);
end;
var
caller: specialize TCaller<string,’hello’>;
begin
caller.Say;
Regards,
Ryan Joseph
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