Re: "Must instantiate controlled types at library level." Why?

[Martin Krischik <krischik@users.sourceforge.net>]

Peter C. Chapin wrote:

> Martin <krischik@users.sourceforge.net> wrote in
> news:2780491.NPbR8AFya6@linux1.krischik.com:
> A_P : P'Class := P'Class(A_C);
> 
> Is A_C "sliced" into a P (to use a bit of C++ terminology)? I'm not
> certain what declaring A_P as type P'Class is doing for me.

If you think of slice as something being cut away then: No!

P is an definite type. For any definite type the size is know at compile
time.

For any tagged type a 'Class type exists. 'Class are indefinite types (like
String). For any indefinite type the size is may or may not  be known at
compile time and if needed is calculated (by compiler magic) at run time.

The trick is that a 'Class type can contain any type from the class hirachie
it is part of. Thats why they are called class wide.

The compiler will calculate the size of C at and make enough space on the
stack so that C can be copied into P'Class.

I almost never use pointers in Ada since I can pass 'Class types around as I
like.

With Regards

Martin

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