Subject: Re: [boost] [Fit]Â formal review starts today
From: Paul Fultz II (pfultz2_at_[hidden])
Date: 2016-03-07 22:02:43
On Monday, March 7, 2016 at 2:52:09 AM UTC-6, Edward Diener wrote:
>
> On 3/7/2016 12:15 AM, Paul Fultz II wrote:
> >
> >
> > On Sunday, March 6, 2016 at 9:42:19 PM UTC-6, Edward Diener wrote:
> >>
> >> On 3/3/2016 6:43 AM, Vicente J. Botet Escriba wrote:
> >>> Dear Boost community, sorry for the late anounce
> >>>
> >>> The formal review of Paul Fultz II's Fit library starts today, 2nd
> March
> >>> and ends on 13th March.
> >>>
> >>> Fit is a header-only C++11/C++14 library that provides utilities for
> >>> functions and function objects.
> >>
> >> These are some comments/queries about the Fit documentation.
> >>
> >> Introduction
> >>
> >> The introduction says that Fit "provides utilities for functions and
> >> function objects." But it seems as if Fit works only with lambda
> >> functions and function objects.
> >
> >
> > Fit works with any generalized Callable:
> >
> > http://en.cppreference.com/w/cpp/concept/Callable
>
> Please document this. A generalized Callable is a much bigger set of
> functionality than just lambda functions and function objects.
>
> >
> >
> >> The term 'function' normally encompasses
> >> a much larger definition in C++ which includes global functions, static
> >> functions, member functions, and lambda functions.
> >
> >
> > Which is what Callable encompasses, but I used "function" since more
> > people are familiar with that than Callable.
>
> A 'function' and a Callable in C++ are two entirely different things.
> Use the one that is precise and don't worry what people are familiar
> with. Explain what a Callable is early on ( I know you explain it later
> ) if you feel that people do not know what it means.
>
> >
> >
> >> Fit needs to be more
> >> precise in what it says it works with. It repeatedly refers to function
> >> objects and lambda functions as 'functions'. I think this vagueness of
> >> terminality is really confusing in the documentation.
> >>
> >
> > Perhaps, I should refer to the Callable concept early on then.
>
> See above.
>
> >
> >
> >>
> >> Quick Start:Function Objects
> >>
> >> "We can make it behave like a regular function if we construct the
> class
> >> as a global variable."
> >>
> >> What about a non-global
> >>
> >> sum_f sum = sum_f();
> >>
> >> makes 'sum' not behave like a regular function other than the fact that
> >> the variable 'sum' may eventually go out of scope ?
> >>
> >
> > In C++, a regular function is always global, there is no such thing as
> local
> > function(sans gcc extensions).
>
> My point is that the non-global 'sum' in my example above behaves just
> as much like a regular function as your global 'sum'. You may want to
> promote the idea of global function objects but I think that this is
> personally a bad idea. IMO global variables of any kind are to be avoided.
It is quite common in several modern C++ libraries to declare functions as
global objects. There are many advantages to this. Why do you believe it
should be avoided? Especially since it has the same effect as a free
function.
DO you believe free function should be avoided as well?
>
>
> >
> >
> >>
> >> Quick Start:Lambdas
> >>
> >> Why do we need both BOOST_FIT_STATIC_LAMBDA and
> >> BOOST_FIT_STATIC_LAMBDA_FUNCTION ? I would seem that
> >> BOOST_FIT_STATIC_LAMBDA_FUNCTION would be adequate and
> >> BOOST_FIT_STATIC_LAMBDA is just redundant, mimicking lambda syntax to
> no
> >> purpose.
> >>
> >
> > BOOST_FIT_STATIC_LAMBDA_FUNCTION and BOOST_FIT_STATIC_FUNCTION both
> define a
> > function at global scope, and can only be used at global scope, whereas
> > BOOST_FIT_STATIC_LAMBDA can be used to constexpr initialize local
> variables
> > as
> > well.
>
> It might be good to add that when the end-user first encounters
> BOOST_FIT_STATIC_LAMBDA, because the name does not suggest
> initialization of local objects. Furthermore I cannot imagine why one
> would want to use it to initialize a local object,
Really? You just said that you would prefer avoiding global functions.
> so you might want to
> explain the benefit of doing so as opposed to the normal syntax for
> creating a lambda function.
>
Maybe the quick start guide isn't the place for this in the first place.
>
> > In fact, BOOST_FIT_LIFT uses this since it is not always clear what
> > context the user might call BOOST_FIT_LIFT.
> >
> >
> >>
> >> Quick Start:Overloading
> >>
> >> The overloading adaptors show two or more lambda functions. Can they
> >> also work with function objects ? Or a mix of lambda functions and
> >> function objects ? In fact all the reamining Quick Start topics show
> >> examples with lambda functions. Do they also work with function objects
> ?
> >>
> >
> > Yes it can be used with function objects. I probably should show an
> example
> > of
> > that as well. I used the lambdas because of the terseness of them.
>
> Evidently the adaptors can be used with any Callable. I think you should
> make that point very strongly and show that in examples also.
>
Agreed.
>
> >
> >
> >>
> >> Quick Start:Variadic
> >>
> >> I do not understand what 'We can also make this print function
> varidiac,
> >> so it prints every argument passed into it.' means ?
> >>
> >
> > I'll try to explain that better, but basically it will print each
> argument,
> > so:
> >
> > print("hello", 5); // Will print "hello" and 5
>
> I wouldn't associate that with the word 'Variadic' but I do think you
> need to explain that more clearly.
>
I always understood variadic to mean taking a variable number of
arguments. What do you understand variadic to mean?
>
> >
> >
> >>
> >> I do not think the Quick Start explains very much since it is dealing
> >> with adaptors of which we know almost nothing and the explanation for
> >> these adaptors and what they actually do is very terse.
> >
> >
> > Probably can expand the explanation of adaptors a little more.
>
> Good idea. What do adaptors create ?
They create a function.
> Different function objects I would
> imagine ? In that case how about the explanation that adaptors take
> Callables as input and generate function object types that adapt the
> original functionality of one or more Callables to some other purpose.
>
The examples are already show taking Callables. Are you suggesting I
show an example taking a member function or something?
>
> >
> >>
> >> In the 'Signatures' section of the Overview I read:
> >>
> >> "All the functions are global function objects except where an explicit
> >> template parameter is required." I honestly don't know what this is
> >> supposed to mean. Does this refer to when function objects are referred
> >> to as parameters to the adaptors, functions, and utilities of the
> library
> >> ?
> >>
> >
> > I don't understand what you are asking. It means that the function is
> > written
> > like this in the documentation:
> >
> > template<class IntegralConstant>
> > constexpr auto if_(IntegralConstant);
> >
> > But its actually a function object like this in the code:
> >
> > struct if_f
> > {
> > template<class IntegralConstant>
> > constexpr auto operator()(IntegralConstant) const;
> > };
> > const constexpr if_f if_ = {};
> >
> > However, `if_c` is written like this in the documentation:
> >
> > template<bool B, class F>
> > constexpr auto if_c(F);
> >
> > It requires the bool `B` template parameter explicity. So in the code it
> is
> > written as a function and not as a function object.
>
> I don't understand to what you are referring when you say 'function'.
> Are you talking about adaptors in your library, functions in your
> library, or what ?
I am talking about all functions that are defined in the library, that
includes adaptors as well. I am not sure how to make that clearer.
> Please try to understand that your use of the word
> 'function' is very broad but that the word 'function' in C++ has a much
> narrower meaning.
>
By function, I mean something like in the example:
template<class IntegralConstant>
constexpr auto if_(IntegralConstant);
I think everyone agrees that is a function in C++.