[boost] Re: Assignment library: review

From: Vladimir Prus (ghost_at_[hidden])
Date: 2004-04-12 05:01:57

Hi Thorsten,

>> Looking at the code, it seems boost::bind uses non-const reference for
>> operator() -- the actual forwarding -- and by-value for arguments to
> 'bind'
>> itself.
> 
> I must admit I don't get that. I extended rhe example to show the problems
> (see attachment).
> As you point out, bind() *silently* compiles code that would not compile
> if one called the original function with those arguments. IMO, *very*
> trouplesome. 

What I was saying is that bind uses non-const reference for operator(), so 
if you use:

    bind(foo, _1)(i);  
    bind( foo, _1 )(ci); 

then it will work ok. In fact, first one compiles and the second one does
not. And, BTW, "foo(i)" compiles just fine too, so your 'proper_forward(i)'
should compile too, but it does not. As for

    bind(foo, i)();
    bind(foo, ci)();

I don't have any opinion yet.

 >> What I think about it is that const-reference prevents you from passing
>> non-const references to constructors of objects you put to container.
> 
> only in the sense that you need to use boost::ref<>

Ah, since you only forward arguments boost::ref<> will work transparently
and you never need to unwrap_reference in the library code.

>>OTOH,
>> with non-const references you'd break the passing of integer literals --
> 
> any "literal", in fact.

Yes, I've used "integer" for example only.

>> Maybe, you really should support ref<> for passing non-const references.
> 
> Depends on what you mean by support :-) It's already supported by using
> ref<>. I think
> that is ok; afterall, reference arguments should not be used that much
> thoughout code.

I agree. In fact, my previous post was just a long-winded way to say that
while in general non-const references might be preferrable, for this
library const references are better.

- Volodya