Re: numbers as 'generics' parameters

[Maciej Sobczak <see.my.homepage@gmail.com>]

On 18 Maj, 16:52, "Dmitry A. Kazakov" <mail...@dmitry-kazakov.de>
wrote:

> generic
>    N : Natural;
> package Strings_Nobody_Ever_Needed is
>    type Pascal_String is new String (1..N);
>    procedure Foo (L, R : Pascal_String);
> end Strings_Nobody_Ever_Needed;

No. The package is already written and no code can be added.
A child package would do, perhaps?

Note also that the constraint to have equal strings is only an example
and probably does not show the full problem.
I might have written my code like this instead:

template <size_t N>
void foo(const fixed_size_string<N> & s1,
         const fixed_size_string<2 * N> & s2);

and it would ensure *at compile time* that the second string is twice
as long as the first one. It should be obvious now that such a
constraint can be anything that is computable (at compile time).
What about this?

(again: the package in question is read only)

> If you replaced the type declaration in Strings_Nobody_Ever_Needed to
>
>    subtype Pascal_String is String (1..N);
>
> you would start to see what's wrong with all this... (:-))

No, I don't follow. Could you please explain?

> Talking about strings, they are allowed to have statically unknown length

Yes - the string was only a vehicle to show the problem. It might be a
matrix of size N or just about anything else.

--
Maciej Sobczak * www.msobczak.com * www.inspirel.com