Re: Copy vector in Ada

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

Le Wed, 07 Nov 2012 14:09:47 +0100, Dmitry A. Kazakov  
<mailbox@dmitry-kazakov.de> a écrit:

> On Wed, 07 Nov 2012 13:03:08 +0100, Georg Bauhaus wrote:
>
>> On 06.11.12 20:47, Yannick Duchêne (Hibou57) wrote:
>>> Now, talking about proper naming of things, how would you explain to a
>>> student, that sometime “type” must follow the substitution principle,  
>>> and
>>> sometime, it do exactly the opposite?
>>
>> The challenge is to explain why the substitution principle is
>> a valid commandment:
>
> It is not.
>
> Positive is a legitime subtype of Integer even though violates the LSP.

That's precisely what was said: both must not be confused.

> The valid proposition is that you should not substitute something
> non-substitutable, but you cannot enforce that through types. Correctness
> cannot be ensured through type checks.

Yes, but just like typing fails to ensure all of the correctness in the  
large (and in some very few cases, even fails to accept valid things).  
That's still the best balance we get between handy and safe.


-- 
“Syntactic sugar causes cancer of the semi-colons.” [1]
“Structured Programming supports the law of the excluded muddle.” [1]
[1]: Epigrams on Programming — Alan J. — P. Yale University