Re: [boost] [Boost-users] [Fit]Â formal review starts today

Subject: Re: [boost] [Boost-users] [Fit] formal review starts today
From: Vicente J. Botet Escriba (vicente.botet_at_[hidden])
Date: 2016-03-09 13:43:53

Le 09/03/2016 09:13, work a écrit :
> On 2016-03-09 18:34, paul Fultz wrote:
>>> On Tuesday, March 8, 2016 4:58 PM, Vladimir Batov 
>>> <Vladimir.Batov_at_[hidden]> wrote:
>>
>
>>> ... a functor. I
>>> think it happens pretty much automatically.
>>
>> Well, the library provides help for that as well, because currently 
>> in C++ you
>> can't pass generic functions to other functions, like this:
>>
>> std::accumulate(v.begin(), v.end(), 0, std::max); // Compile error
>> However, BOOST_FIT_LIFT will let you do that:
>>
>> std::accumulate(v.begin(), v.end(), 0, BOOST_FIT_LIFT(std::max));
>
> Isn't it resolved with
>
> std::accumulate(v.begin(), v.end(), 0, boost::bind(std::max<int>, _1, 
> _2));
>
> Seems like std binders take care of the generic functions' 
> "awkwardness". Am I missing anything?
I want to type

   std::accumulate(v.begin(), v.end(), 0, std::max);

There is a proposal that will make this code correct.

I believe that the closest to that is

   std::accumulate(v.begin(), v.end(), 0, OSAFA(std::max));

Where OSAFA mean Overload Set As Function Arguments [1] . The macro 
BOOST_FIT_LIFT tries to go in this direction.

You can always continue to use bind, but I prefer to don't have to add 
the <int> annotation.

As said before, I'm for the use of macros when we have a future language 
feature. We need to find a good name.
A user is not forced to use the macro if this goes against its style or 
company coding rules/guidelines.

>
>>> "if we construct the class as a global variable"
>>>
>>> Should I be excited about it? Globals are often a royal pain. Do I want
>>
>>> to construct it a a global variable?
>>
>> Whats the pain about these Global variables? They are const, can be
>> namespaced, and work just like free functions. However, they do have 
>> several
>> advantages.
>
> I much prefer creating things locally to minimize the scope and the 
> potential for mis-use. If I (or someone) create something (an object), 
> there is a potential desire to stick some stateful info/data into it. 
> Then, the complexity snow-balls as it becomes a bottleneck in 
> multi-threaded env.
I believe that the library should NOT promote global functions or 
variables. The library should just provide some mechanism that help to 
define those global functions. IMO, most of the documentation should 
ignore all these STATIC macros.
>>
>> First, by making them objects we can turn functions into first-class 
>> citizens.
>
> Why can't I use the standard binders to achieve that?..
You can.
> Or what do I gain by using Fit instead?
This is better question.

I believe that we need to see the Fit library as two different concerns:
HOF * provide some high order functions that are useful when doing 
functional programming
SHOF * provide some mechanisms that help to define global high order 
functions

You can ignore the second part (SHOF - static high order function) if 
you don't want to define global high order functions or if you prefer to 
define a function object to this end.

The first part HOF, includes a lot of useful functions. IMHO the library 
need yet some modifications here and there, but I find that there is an 
added value for those that want to use functional programming.

>
>> skipped considerable chunk...
>
> What I seem to hear is that Fit helps to overcome some plain-function 
> limitations. I think you might want to consider highlighting what Fit 
> adds compared to the standard binders. I felt that quite a few of your 
> examples could be done using those binders. I might be wrong though.
>
I don't think you can do all with binders, but maybe I'm wrong. Bind is 
a way to transform a non high order function on one that is high-order.
Maybe you can show how binding can be used to define some of the 
function the library provides, compose, fix, flow, ...match, partial, 
for example.

We need to have more functions and ways to compose them. Fit goes in 
this direction.

Best,
Vicente

[1] http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2016/p0119r1.pdf