Re: Using Red-Black Trees

["Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>]

On Thu, 18 Nov 2010 13:36:57 +0100, J-P. Rosen wrote:

> Le 18/11/2010 10:02, Dmitry A. Kazakov a �crit :
>>> 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;
>> 
>> Yes of course it is a simple, but non-Ada solution. BTW, I am using it for
>> years, with a small addition that the implementation is selected by the
>> gpr-file.
>> 
>> But it is not Ada it is pure C, because nothing is checked. 
> Come on, any incorrect usage will not compile!

So is any incorrect usage of a C++ template. It is exactly the same use
case. The point is that the implementation shall be checked when compiled,
separately from the instantiation/use point(s).

> You may argue that it would be nice to check that both structures are
> compatible, but I challenge you to define the compatibility rules for
> packages. In practice, two packages are compatible if the *user* uses
> only compatible subprograms from both...

Rules similar to ones for matching formal generic parameters should
suffice.

I don't think this is a problem. What is a potential problem is children
packages, i.e. children of abstract packages vs. children of their
implementations and how they mess up with each other.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de