Re: Understanding generic package functions

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

On 11/03/2015 12:59 AM, Nick Gordon wrote:
> 
> Oh! I see! Suddenly this makes much more sense. I appreciate this a lot! I
> see that it wasn't the declaration of Ada.Numerics.e that was the issue, but
> the generic package. How though do I use the overridden binary operator ** in
> that case? Do I call X MyPack."**" Y or is there some way for me to inform
> the compiler do it, like use MyPack;?

You have a number of options.

1. Full dotted name. An operator is a function just like any other function, and
can be called just like any other function:

Math."**" (X, Y)

2. Renaming.

function "**" (Left : Float; Right : Float) return Float renames Math."**";

This lets you use "**" as an infix operator: X ** Y

3. A use clause.

use Math;

This also lets you use "**" as an infix operator: X ** Y

The use clause gives you direct visibility to everything in the public part of
the pkg spec. Sometimes that's not desirable. I tend to avoid use clauses, since
they often make code harder to understand. I won't object too much for pkgs in
the standard library or for a limited scope with lots of references.

Not applicable in this case, but when a package declares a type and operations
on the type, you can use a "use type" clause

use [all] type Package_Name.Type_Name;

This gives direct visibility to the operators for Type_Name but not for anything
else in the pkg. If "all" is included, it makes some other things directly
visible, too, of which enumeration literals are the most commonly used.

-- 
Jeff Carter
"Drown in a vat of whiskey. Death, where is thy sting?"
Never Give a Sucker an Even Break
106