RE: [boost] function.hpp: some ideas

From: Geurt Vos (G.Vos_at_[hidden])
Date: 2001-05-04 03:07:31

8<snip>8

> > When there's no op=(const Functor &), assignment to
> > 0 will call op=(const assign0 *). Assignment to a
> > functor/function will simply call the (non-explicit)
> > templated constructor.
>
> Ah, interesting. We'd pay for this usefulness in efficiency, however,
because
> the extra copy would require another memory allocation and deallocation.
I'm
> not sure the cost is worth it.

Well, you could use reference counting :)

> The general feeling was that the "f = 0"
> syntax was less obvious than "f.clear()" (even though it mimics function
> pointer syntax better), so it would be tough to convince the general
populace
> that this change is worth it.
>

Hmm, I would say if I can assign a function pointer, it is
only natural that I can also assign 0. Additionally, since
'if (f)', or  better 'if (f !=/== 0)' is possible, it again
makes 'f = 0' an obvious possibility.

Then to clear, everyone will understand what will happen
when clear() is called. However, its counterpart: set() does
not exist, which might be seen as not-really-consistent.

Note that I'm not saying support for 'f = 0' is crucial, I'm
just saying that IMO 'it's not obvious' is not a very strong
argument.

>
> If assign0 is hidden in a detail namespace, user's know they've been
warned
> not to dig that far into Boost internals. Note that the same thing done
for
> "nil" here is done for "ignore" in the tuple code.
>

One should not repeat the errors of the past...
...but seriously, 'nil' specifically for 'function' doesn't
feel right. There's nothing 'function' about 'nil'. I mean,
'nil' on its own is not related to function (at least that
is not how the user will see it). Having a general boost::nil
in e.g. nil.hpp or whatever sounds (somewhat) better.

Geurt