[fpc-devel] Abstract generics

[Simon Jackson]

Further to the ranges in generics discussion....... more on generics

There is always a way to do that using an abstract class. The things of interest creating the idea are:

1. Imagine a short hand syntax for abstract classes:

Generic classAbs<T> = class(TObject)
Class generic variable: TObject;
End;

abClass = specialize classAbs<abstract>;

// This allows a short hand, and

2. Some possible crazy inheritance:

Generic classAbs<T,Q> = class(Q)
Class generic variable: TObject;
End;

abClass = specialize classAbs<Integer, abstract>;

// which allows a form of polymorphic inheritance similar to interfaces, but short hand for interface variables.

3. Some code optimization for less cache thrashing

Class generic procedure classAbs.doSomething(T);
//generic procedure x.y(T); this also
Begin
// enforce no usage of field and methods on T, such as T.specificToClass()
// allows same piece of code to be used for all types of same sizeof()
// so less code to fill the L1 instruction cache, and the L2 cache is less burdened
// of course this speed and code size optimization could be detected without this
// but enforcing it could always be an option.
End;

4. Compile time virtual kind of resolution

// As an abstract class would have many virtual abstract methods there would be a pointer indirection from the VMT.
// Any generic procedure or method could, if not virtual, be compiled in and so not need a virtual specifier.

[Sven Barth via fpc-devel]

Post by Simon Jackson
Further to the ranges in generics discussion....... more on generics

I've already mentioned my reasons against that. So throwing around strange
syntax extensions does not help. At all.

Regards,
Sven