Re: Problem with generic linked list package

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

On 08/09/2014 07:32 AM, Laurent wrote:
>
>     with function "<"(Left, Right : Element) return Boolean is <>;
>     with function "="(Left, Right : Element) return Boolean is <>;
>
> There is no "<" and "=" defined for Element_Type, normally. So the "<>" seems to do the trick but why?
> The box tells the compiler that it will get the info it needs later. But in this case there is no later, isn't it?

The box means, if no explicit actual subprogram is provided, and there is 
visible at the point of instantiation a subprogram with the same name and the 
same parameter and return type profile (substituting the actual for Element), 
then the instantiation will use that visible subprogram.

You can still provide an explicit actual subprogram:

"<" => "<"

"=" => Equal

Now, suppose you have a type T for which "<" is not meaningful. You want to have 
a linked list of T, but will never use Insert_In_Order. Can you still use your 
package to do this? If not, how could you change your package to support this, 
while still providing Insert_In_Order for types with "<"?

-- 
Jeff Carter
"Insufficient laughter--that's grounds for divorce."
Play It Again, Sam
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