Re: Is this a bug?

[Stephen Leake <stephen_leake@acm.org>]

Brian May <bam@snoopy.apana.org.au> writes:

> So another words, if I did the following:
> 
> declare
>    ...
>    Current : Bucket_Access renames Current_Hook.all;
> 
> begin
>    ...
>    Current_Hook := <something else>
>    ...
> end;
> 
> 
> Then Current would still be the same object and value it use to be?

Yes, you have it right.

> If so, then "renames" isn't quite as simple as I thought. 

You are not alone; it seems to be a common misunderstanding for people
learning Ada.

> It is more like a "hard link" then a "symbolic link". i.e. it links
> to the object rather then the name of the object. Interesting.

The purpose of "renames" is to cache the results of computing a
complex name. Although sometimes we think of it as just "cleaning up
the code", it can produce significant time and code space
optimization.

If you want a short name for a complex expression, that is re-evaluated
each time the name is used, you need a function, not a rename:

declare
    function Current is return Current_Hook.all; end Current;
begin

Only 3 more identifiers!

> Question: If you freed the value (with unchecked_deallocate) of
> "Current_Hook" would the value of "Current" still be valid? I
> suspect it would not be valid, as "Current" is now dangling. 

Current would be invalid.

-- 
-- Stephe