Re: A bad counterintuitive behaviour of Ada about OO

["J-P. Rosen" <rosen@adalog.fr>]

Le 07/08/2014 22:29, Shark8 a écrit :
> On 07-Aug-14 07:34, J-P. Rosen wrote:
>> Classification makes sense only if you have
>> heterogeneous data structures that manipulate various types belonging to
>> a same class.
> 
> I'd note that the heterogeneous data-structure needn't be strict;
> consider if you will an instruction set for a [virtual] CPU -- different
> instructions could have different numbers of parameters and therefore
> not be [strictly] heterogeneous. (Granted that all of these instructions
> would have another, if implicit, common parameter: the CPU.)
> 
> So, you could end up with abstract types:
>   Instruction         -- Base/common interface.
>   Arity_0_Instruction -- Common structure of 0 param instructions.
>   Arity_1_Instruction -- Common structure of 1 param instructions.
>   Arity_2_Instruction -- Common structure of 2 param instructions.
>   Arity_3_Instruction -- Common structure of 3 param instructions.
> and having all the instructions derive from the proper Arity.
> 
> Granted, you could also do the above [structurally] using a
> variant-record with multiple nestings.

Exactly. In Ada, you have multiple solutions to a problem (like using
plain types, variant types, tagged types, generics), with different
trade-offs, and it is the basis of engineering to investigate and choose
the most appropriate solution for the case at hand.

That's what I like with Ada, and that's why I regularly object to the
argument that "you can do everything with OOP, therefore you must do
everything with OOP".

-- 
J-P. Rosen
Adalog
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