Re: Traits and iterators (was: Mixing operators and dot notation)

[briot.emmanuel@gmail.com]

> generic
>     with package Elements is new Elements_Policy (<>);
>     type Container is private;
>     type Cursor is private;
>     with function First (Self : Container) return Cursor is <>;
>     with function Has_Element
>        (Self : Container; C : Cursor) return Boolean is <>;
>     with function Element (C : Cursor) return Elements.Element is <>;
>     with procedure Next (C : in out Cursor) is <>;
> package Forward_Cursors_Policy is
> end Forward_Cursors_Policy;
> 
> That, in itself, I don't think will give the ability to use "of" in 
> iterations, although it enables one to iterate over an unknown type.


Indeed, this signature package allows you to write an explicit iteration loop, where
you manipulate cursors explicitly. I don't know, and I don't think it is doable, how to
pass a formal type and mention that it should be iterable in the sense of the "for..of"
loop.
That means that any generic algorithm we write will take the above Policy package,
but will not be able to use "for..of". That's a bit more work to write, but just as
efficient in the end, but perhaps a limitation in the language.