Re: Ada.Containers.Doubly_Linked_Lists

[Niklas Holsti <niklas.holsti@nospam.please>]

Carroll, Andrew wrote:
> Hello,
>  
> I would like to understand how to use the Ada.Containers.Doubly_Linked_Lists
> package.  After I with Ada.Containers.Doubly_Linked_Lists and then
> declare a variable x: Ada.Containers.Doubly_Linked_Lists.List I get
> the error:
>  
> invalid prefix in selected component "doubly_linked_lists".
>  
> So, what I'm saying here is that I have no clue how to use the
> Ada.Containers.Doubly_Linked_Lists package and I'm hoping that
> someone here can show me how to use it.

The packages in Ada.Containers are "generic" packages, so you first have 
to make an "instance" of Doubly_Linked_Lists before your program can 
declare list variables. When you make an instance, you specify which 
type of elements the list can hold (Element_Type) and how to compare two 
elements for equality (the "=" operator for Element_Type).

See http://en.wikibooks.org/wiki/Ada_Programming/Generics for 
explanation and examples of generic packages, and 
http://www.adaic.com/standards/05rat/html/Rat-8.html for specific advice 
on Ada.Containers.

For example, here is how to make a package that manages lists of Integers:

    with Ada.Containers.Doubly_Linked_Lists;
    ...

    package Integer_Lists is
       new Ada.Containers.Doubly_Linked_Lists (
          Element_Type => Integer);

(I did not give any actual for the formal "=" operator because it 
defaults to the predefined "=" for comparing Integers.)

And here is how to declare a variable that holds a list of Integers:

    Ints : Integer_Lists.List;

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
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