Re: Announce: Grace project site operational

[Jeffrey Carter <jrcarter@acm.org>]

Ted Dennison wrote:
> 
> Jeffrey Carter <jrcarter@acm.org> wrote in message news:<3CDD75C7.36C6ADCF@acm.org>...
> > The imported type Element should have the "=" operation imported for it.
> >
> > The "=" operations for types List and Iterator should be visible to
> > clients of the package.
> 
> I'd like to see more discussion on this point. The way I remember it,
> we didn't want to add a lot of generic parameters that >%99 of the
> time would not be used. I can't remember overloading "=" myself, ever.
> This goes back to the "default generic parameters" issue, but I
> digress. However, I seem to remember some folks saying that not
> importing "=" this way causes the built-in equality to reassert itself
> even after its been overridden. Am I remembering this correctly?

Yes. For this to be a general-purpose package, it should work correctly
if the client has a user-defined "=" for the actual type used for
Element. Since the package does use "=" for this type (in "=" for List),
it must be imported to work properly.

Luckily, we can default subprograms ("is <>"), so this adds no
additional burden to the instantiation for most users.

Since types List and Iterator are private, we are telling the client
that "=" for these types is meaningful. Since the predefined "="s for
these types are not meaningful, that means the client must have
visibility to the package-defined versions. Currently these versions are
declared in the private part of the package, so the client does not have
visibility to them. They should be moved to the visible part of the
specification so the client may call them.

-- 
Jeff Carter
"Now go away or I shall taunt you a second time."
Monty Python & the Holy Grail