Re: [boost] [review][Fit] Review of Fit starts today : September 8 - September 17

Subject: Re: [boost] [review][Fit] Review of Fit starts today : September 8 - September 17
From: Edward Diener (eldiener_at_[hidden])
Date: 2017-09-16 19:31:33

On 9/16/2017 2:14 PM, P F via Boost wrote:
> 
>> On Sep 15, 2017, at 8:46 PM, Edward Diener via Boost <boost_at_[hidden]> wrote:
>>
>> On 9/8/2017 7:02 AM, Matt Calabrese via Boost wrote:
>>> A formal review of the Fit library developed by Paul Fultz II starts
>>> today, September 8, and runs through September 17.
>>> A branch has been made for the review. You can find Fit for review at
>>> these links:
>>> Source: https://github.com/pfultz2/Fit/tree/boost <https://github.com/pfultz2/Fit/tree/boost>
>>> Docs: http://pfultz2.github.io/Fit/doc/html/doc/ <http://pfultz2.github.io/Fit/doc/html/doc/>
>>
>> I have some questions about Fit which I can not understand by reading the docs:
>>
>> 1) Does Fit functionality work only with function objects as opposed to callables in general ?
> 
> In general yes, but its not the case for every adaptor.

OK.

> 
>>
>> 2) Is the purpose of BOOST_FIT_STATIC_FUNCTION only to create a function object at global or namespace level ?
> 
> Yes.

OK.

> 
>>
>> 3) Does BOOST_FIT_STATIC_FUNCTION only accept a function object or does it accept any callable ?
> 
> It only works with function objects, which I should document its type requirements.

Please do.

> 
>>
>> 4) The documentation says that "BOOST_FIT_STATIC_LAMBDA_FUNCTION can be used to the declare the lambda as a function". I am not sure what this actually means since a lambda function is a function.
> 
> Maybe that could be worded better, but it lets you declare the lambda at global or namespace scope.

OK.

> 
>>
>> 5) I do not understand the purpose of the pipable adaptor. What is the point of using it ? It is mentioned as an alternative to Unified Call Syntax but, while I understand the latter, I do not understandable how pipable allows "extension methods", which is a large part of the purpose of UFCS.
> 
> That is, you want to add an extension method to a class so it can be called as `x.f(y)`. With UFCS, you can just declare a free function called as `f(x, y)` and then call it as `x.f(y)`, with the Fit library you would declare the function as pipable and then call it as `x | f(y)`.
> 

Let us suppose I have a class:

struct X { some member functions etc. };

Then I want to add a member function to class X with a prototype called 
void f(int) so I can call it as an extension method without modifying X. 
With UFCS in effect I create the free function:

void f(X px,int py) { some implementation }

and now if I have:

X x;

I can call:

x.f(3); // Works with UFCS support

successfully. Could you please show me the equivalent code that uses 
pipable in this same scenario ?

>>
>> In general I am confused by what the requirements of Fit adaptors are.
> 
> Which ones?
> 
>> This may be because the terms "function objects" and "functions" are used in a way which does not follow standard C++ terminology as far as I know it.
> 
> The type requirements for the adaptors are documented as either `ConstCallable` or `ConstFunctionObject`, which follows standard C++ definitions with an additional `const` requirement.

OK.

Thanks !

> 
> 
> 
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