[fpc-devel] New feature announcement: constant parameters for generics

[Sven Barth]

Am 26.04.2020 um 23:42 schrieb Benito van der Zander:
> Hi Sven,
>
>>
>> It's not that simple. In principle you're right that the compiler 
>> could try to merge more implementations, but this does not depend on 
>> the declaration of the generic, but the use of the parameter types.
>
> I mostly use generics for containers, especially hashmaps. They only 
> stores the values and never calls specific methods on them
>

Well, nice and well for /you/ then, but there are many more uses for 
generics. And as a compiler developer I /must/ think about these cases 
as well.

>>
>>
>> Not to mention that your TBaseHashMap would not work with managed 
>> types...
>
> That would need be handled separately. There are probably also people 
> who want a container that calls .free on TObject descendants.

The user should not need to care about that, especially for general base 
classes.

Also assume you have a record and a hashmap that stores them. Now you 
add a string to the record which turns it into a managed one and 
suddenly your code will no longer work, probably resulting in subtle 
bugs or memory leaks. That's /not/ what should happen for merely adding 
a string. It's already bad enough that this happens with the Pascal 
style I/O we don't need to have this with base container types.

For calling Free we have explicit classes. But the difference between 
managed types vs. not-managed types is subtle and can change - as 
mentioned above - by merely adding a field.

Regards,
Sven
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