Re: Using Red-Black Trees

["Yannick Duchêne (Hibou57)" <yannick_duchene@yahoo.fr>]

Le Thu, 18 Nov 2010 07:27:20 +0100, J-P. Rosen <rosen@adalog.fr> a écrit:

> Le 18/11/2010 00:39, Yannick Duchêne (Hibou57) a écrit :
>> You can have only one at a time. If you select an implementation, you
>> select it system-wide, and you cannot select one for that usage and
>> another for another usage in the same system.
>>
> If that's really what you want, there is an easy solution.
> Provide two packages with identical (or compatible enough for your
> purpose) specifications:
>
> package Binary_Tree is....
> package Linked_List is....
>
> Then declare at library level:
> with Binary_Tree;
> package My_Structure renames Binary_Tree;
>
> And then, use My_Structure all over the place. By changing two words in
> one two-line file, you can switch your entire project to the other
> implementation.
I know that one, but this is a workaround, not a language support (the so  
called “static polymorphism”). Formally speaking, you do not have multiple  
implementations of a single specification. The closest thing actually is  
generic package. But that is not easy to do with generics: you will have  
to give the generic instance all of its custom implementation via generic  
parameters (methods and others).


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