Re: [boost] [Fit]Â formal review starts today

Subject: Re: [boost] [Fit] formal review starts today
From: Paul Fultz II (pfultz2_at_[hidden])
Date: 2016-03-05 11:07:31

On Saturday, March 5, 2016 at 6:22:53 AM UTC-6, Peter Dimov wrote:
>
> Rob Stewart wrote: 
> > On March 4, 2016 3:27:08 PM EST, Paul Fultz II <pfu..._at_[hidden] 
> <javascript:>> wrote: 
> > > 
> > > The library could switch to using `Callable`, if everyone feels that 
> is 
> > > better. However, I honestly prefer to make mutable explicit. I would 
> > > like to hear feedback from other reviewers as well. 
>
> I do not object to your requiring ConstCallable. I made boost/std::bind 
> const-neutral because this felt the right thing to do - it's not bind's 
> job 
> to tell you what your function object ought to do, it just reflects 
> whatever 
> it does. At the same time, stateful function objects do have limited 
> applicability outside of for_each which specifically guarantees order and 
> returns the function object. You could pass bind( ++_1, 0 ) to generate_n 
> and that's pretty much it. 
>
> So I do not see the requirement as a defect warranting rejection. If users 
> demand Callable support, you'll add it. If not, not. 
>
> > If your library only requires Callable, then users can supply a Callable 
> > or a ConstCallable. When you require a ConstCallable, they cannot supply 
> a 
> > Callable. There may be valid reasons for that restriction in certain 
> > cases, but they should be documented rather than just imposed as a 
> > convention. 
>
> That's true in principle. In practice though function objects that are not 
> ConstCallable are in 90% of the cases the result of a forgotten 'const' on 
> operator() and not a deliberate decision. So requiring ConstCallable 
> catches 
> errors. 
>

Furthermore, when I've needed a mutable function objects, many times I've
needed to use `std::ref` to get the proper behavior.