Re: Array Index: substitute integer with enumeration

["Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>]

On 6/4/20 6:54 PM, hreba wrote:
> 
> function To_Spherical (p: Point) return Point is
>    pc: Cart_Point:= p;
> begin
>    return
>      ( Sqrt(pc(x)**2 + pc(y)**2 + pc(z)**2),    -- r
>        Arctan(p(y)/p(x)),            -- phi
>        ...
>      )
> end To_Spherical.
> 
> My questions are now:
> 
> 1. Does the initialization of pc involve any copying at run time?

1. If you can get your code to compile, you can check the object code to see.

The only reason for worrying about this is if it causes Storage_Error or failure 
to meet your quantitative timing requirements. Since you haven't tried it, you 
don't know that will happen, so there's no reason for concern.

Seems to me that with a design like

package Cartesian is
    type Point is record
       X : Float := 0.0;
       Y : Float := 0.0;
       Z : Float := 0.0;
    end record;

    -- Operations of Point

    generic
       type Client_Point is private;
       with function To_Cartesian (P : Client_Point) return Point;
       with function To_Client (P : Point) return Client_Point;
    package Client is
       -- Operations of Client_Point
    end Client;
end Cartesian;

type Point is record
    R     : Float := 0.0;
    Phi   : Float := 0.0;
    Theta : Float := 0.0;
end record;

function To_Cartesian (P : Point) return Cartesian.Point;
function To_Spherical (P : Cartesian.Point) return Point;

package Spherical is new Cartesian.Client (Client_Point => Point,
                                           To_Cartesian  => To_Cartesian,
                                           To_Client     => To_Spherical);

copying would not be a concern.

-- 
Jeff Carter
"When Bell Labs were invited to evaluate C against the DoD requirements
[for Ada], they said that there was no chance of C meeting the
requirements of readability, safety, etc. for which we were striving,
and that it should not even be on the list of evaluated languages."
William Whitaker
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