Re: [boost] On bind::operator==, again

From: Peter Dimov (pdimov_at_[hidden])
Date: 2004-03-11 10:35:38

Douglas Gregor wrote:
> On Thursday 11 March 2004 06:14 am, Peter Dimov wrote:
>>
>> In fact, I still think that your decision to expose the 'f contains
>> g' operation under the f == g notation is a mistake, too. 'contains'
>> is not '==', either; it is asymmetric, as it is possible for f to
>> contain g but not vice versa.
>>
>> In short, == for function objects is an illusion and it must die,
>> Herb Sutter's influential articles notwithstanding.
>
> Opinion noted :)
>
> The primary reason for using operator== is that it models what
> function pointers do, and makes function<> a near-complete drop-in
> replacement for function pointers. That's been my goal for a Very
> Long Time.

Yes, I understand the Long-Term Goal (if not its utmost importance), but
your approach doesn't scale to other function<>-like entites.

void f();
my_function<void()> g(f);
your_function<void()> h(g);

g == h; //???
g.contains(h); // false
h.contains(g); // true

It's limited to the one and only function<> (and you can't even ask a
function<> whether it contains another function<>, right?)