Re: Converting C++ class to Ada

[Ken Garlington <GarlingtonKE@lmtas.lmco.com>]

Jon S Anthony wrote:
> 
> Two ways:
> 
>   1. type Object_Type (
>          X_Motor : Motor_Access_Type;
>          Y_Motor : Motor_Access_Type;
>          X_Limit : Switch_Access_Type;
>          Y_Limit : Switch_Access_Type ) is null record; (or better: is private)
> 
>   Now, whenever an object of this type is declared, you will have to supply
>   the discriminants and there you are.  Note that this works for the case of
>   _limited_ types too.

However, will I be able to update the discriminants? Norman Cohen points
out that I could have an updatable copy within the record, but
that seems a little clumsy. Also, if I wanted to make sure that "null"
wasn't used as one of the discriminants, would I have to use "access
Motor.Object_Type" rather than the declared access type?

>   2. type Object_Type (<>) is private;
>      function Make (
>          X_Motor : Motor_Access_Type;
>          Y_Motor : Motor_Access_Type;
>          X_Limit : Switch_Access_Type;
>          Y_Limit : Switch_Access_Type ) return Object_Type;
> ...
>  private
>      type Object_Type is record ... as you have it
>         OR
>      type Object_Type (... as in 1.
> 
>   Now, whenever an object of this type is declared you will have to
>   initialize it.  The only way you give is via Make, so you can force
>   the supply of arguments.  This way is especially useful with instances
>   of limited types via allocators as you can have your own pool and know
>   all clients must use that pool.

OK. This looks like it might be a winner. I'll try it and see.

> Right.  Except I don't see this as simply a "style" issue.  It is more
> important than that.  The C++ hack..ah..coder goofed and should have made
> the motor and switch stuff private (or protected).

OK. I'm trying not to stray too far from the C++ code, since I would
like
for C++ folks to be able to compare it with the Ada version, but I think
in this case I'll make an exception and make it private.

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