Re: Q: on redefinition of "=

[bobduff@world.std.com (Robert A Duff)]

In article <4jrsumINN9m0@snoopy.cis.ohio-state.edu>,
david scott gibson <dgibson@snoopy.cis.ohio-state.edu> wrote:
>The strategy I'm currently working with uses null-bodied Initialize
>and Finalize routines for wrapped scalars.  I provide an initial value
>with a record component initialization.

So why use a controlled type?  Perhaps because *some* of your types need
Initialize or Finalize, and you want to inherit from a single root type
which has Swap.  Well, I wonder if you could have a non-controlled root
type with Swap, and extend it with controlled components in the cases
where you need that functionality?

>...  The lack of a valid
>representation is the problem, however, not the lack of a specific
>initial value for scalars.  Since the representations don't have any
>controlled sub-components, I'm assuming that the Initialize and
>Finalize calls for wrapped scalars can be optimized away.

They can, so long as you don't have class-wide stuff.  But I doubt if
they *are*, in a typical compiler.

>...I realize
>the tagged types will require more storage, but does GNAT's
>implementation entail an additional performance penalty in this
>situation?

I believe so.  Every controlled object will be hooked onto a chain
(doubly-linked, I think), of controlled objects.

>>Also, a plain old (non-controlled) record type can have automatic
>>initialization for its components.
>
>Yes, I've still got this implementation around.  It suffers from all
>of the same type conversion annoyances and requires explicit
>importation of Swap everywhere.

...or use "is <>" default for Swap.

>...  However, it should be more efficient.
>Once GNAT is compiling everything, I'll do some performance
>comparisons and get an idea of just how costly the tagged scalars
>implementation is.

- Bob