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

From: Douglas Gregor (gregod_at_[hidden])
Date: 2004-03-10 17:49:58

On Wednesday 10 March 2004 11:27 am, Brian McNamara wrote:
> I don't see why people can't cope with
>
>    delegate<void()> f;
>    handle h = f.connect( some_function_object );
>    ...
>    f.disconnect( h );
>
> instead.  Indeed, it seems to me that it might be cheaper to hold onto
> the handle in some cases rather than the function object.  (A handle
> could presumably be an int, whereas a function object may be many words
> of data or maybe even require heap storage.)  But admittedly, I don't
> typically work in these domains to know how people _actually_ use (or
> want to use) these things.

Oh, I know, and I mostly agree. I tend to liken += and -= to new and delete, 
whereas the handle idiom (they're calling "connections" in Signals) is like 
having a smart pointer. 

> Maybe the best compromise is to define a new entity for "function
> equality".  Define a function (result_of-capable functor, really) like
>
>    boost::function_equal( f, g )
>
> which has this behavior:
>
>  - if f and g are both function pointers, use operator==, else
>
>  - if one or both are user-defined types, call f.function_equal(g)
>    (or g.function_equal(f)) if it exists, else
>
>  - return false (or fail to compile, whichever people decide is best)

We can have boost::function_equal(f, g), but I'd prefer that it always use 
operator==. Then boost::lambda, boost::bind, etc. can just overload 
function_equal. Why? Because most users just want to write a normal 
operator== and have it work; that's what makes sense. Just because Lambda can 
do some screwy things with syntax (and believe me, I love Lambda) doesn't 
mean others should have to use a weird comparison syntax.

        Doug