[setup] Why does PackageSpecification have a private copy-constructor? (Robert?)

[Igor Pechtchanski]

On Mon, 30 Aug 2004, Max Bowsher wrote:

> I can't see why setup's PackageSpecification class has a private
> copy-constructor.
> Am I missing something?

AFAIU from the C++ spec, the copy constructor is needed to pass something
by value.  Making it private disallows passing anything by value, only by
reference.

> The reason why I am suddenly interested is that the C++ standard says that
> this:
>
> foo(SomeClass())
>
> requires SomeClass's copy-constructor to be accessible (bizarre, no?) and g++
> 3.4 has decided to enforce this.

Only if foo()'s signature is

... foo(SomeClass a);

If you declared foo() as

... foo(Someclass const & a);

(see, for example, packagedb::findBinary()), the copy constructor
shouldn't be needed.

> So, unless I can make the copy-constructor public (which I don't want to
> do if doing so risks other problems), I need to rewrite all code like:
>
> do_something(PackageSpecification(somename))
>
> to:
>
> PackageSpecification tmppkgspec(somename);
> do_something(tmppkgspec);
>
> which isn't very nice.

The above is a no-op, since if do_something() takes a PackageSpecification
instance by value, then it would take tmppkgspec by value, and attempt to
copy it, and you're back to the copy constructor problem.

It is *remotely* possible that g++ 3.4 decided to disallow passing newly
created instances by reference, but I haven't used 3.4, so can't say
anything about it.
	Igor
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