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Subject: Re: [boost] [Fit] formal review starts today
From: Peter Dimov (lists_at_[hidden])
Date: 2016-03-05 07:22:26

Rob Stewart wrote:
> On March 4, 2016 3:27:08 PM EST, Paul Fultz II <pfultz2_at_[hidden]> 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

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