Am 06.05.2021 um 17:33 schrieb Ryan Joseph via fpc-devel:
I found something sneaky I'd like to confirm before I decide what to do about
it.
1) "T" in TAnyClass<T> is specialized as Integer from the first parameter with
TSomeClass (which is TAnyClass<Integer>).
2) "U" is getting specialized as String by looking at the parameters in Compare() in
which "U"(the second generic parameter) is String.
This specializes the procedure correctly but it uses a very sneaky method which is very hard to
discern. I feel like that if a generic parameter is already used (like T in specialize
TCallback<T, U>) then no further attempt should be made to look at the parameters and in
the example below "U" would not be found and the function would fail to implicitly
specialize.
There is nothing sneaky if one defines that the parameters are evaluated
left to right and those that are already found and used later on (like
T) are simply fixed then thus in the example it uses the already found
type. But if the picked type wouldn't mach, for example if TCallback<,>
would be declared as TCallback<T: TObject; U> instead then trying to
specialize the function would simply fail.
Regards,
Sven
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