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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.

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