>> >> 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?
Global objects, whether functions or data, increases the chances for name clashes. Also accessing global data increases the chances for errors in a multi-threaded environment.
Free functions can be in a namespace, as the standard library functions are in the 'std' namespace. This helps greatly in avoiding name
conflicts.
By global variables, I mean defined at the namespace level, not solely at the global namespace level. So functions using BOOST_FIT_STATIC_FUNCTION can be defined within a namespace. Also, the function objects are `const` so there isn't an issue from multithreaded environments.
> > >> >> 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.
I mean that for local objects I do not see the reason why I would ever use BOOST_FIT_STATIC_LAMBDA instead of initializing local objects in the normal C++ way(s). If this is not the case you need to explain what problem(s) BOOST_FIT_STATIC_LAMBDA solve in initializing local data which ordinary C++ initialization of local data could encounter. If there aren't any problems BOOST_FIT_STATIC_LAMBDA solves in initializing
local data I see no purpose for its existence.
Well, they can still be passed to constexpr functions, even if they are local, I probably shouldn't discuss BOOST_FIT_STATIC_LAMBDA in the Quick Start guide because its usage is not quite as a common.
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.
I would hope to convince you that a good Overview of your library should come first and then all the Quick Start guides, tutorials, examples etc. would make much more sense once your end-user understands what your
library really does in terms of at least the main general functionality.
I usually start with the Quick Start guide with a library in order to get an understanding of what components are in the library and what they can do, then I start delving into the other components from there. Thats what I am showing in the Quick Start guide. I guess people have different ways of learning a library. I wonder what is needed to be explained better in a initial overview of the library.
> 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?
Your terminology is fine, but I always think of variadic in terms of variadic templates or variadic macros. After all your not making the print function variadic in the sense of taking a variable number of
arguments.
Yes, I am, so I probably need to make that more clear in the documentation.
The simple_print functionality is any of 3 different lambda > functions, with 'conditional' picking the first one that is callable and
'fix' passing in the callable as the first parameter. So I really don't understand what 'by' does here in printing each argument irregardless of
your 'Variadic' terminology. You need invoking examples and then show what the output would be for each invocation, and then it would be
easier for me and others to understand what 'by' does in this situation.
Yep, that part needs to go into more in-depth.
> > >> >> 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?
Global/static function, member function, std::function, boost::function, Boost Phoenix and/or Boost lambda function objects, instantiated template functions. My point is that you should show your library functionality working with as many types of Callables as possible. Instead your doc suggests that function objects and lambda functions are the only type which can be passed to your library's functionality and
you enforce this view by your examples.
I'll try to do that.
> > >> >> 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
> 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++.
I call that a function template.
Which is a family of functions.
My definition for 'function' is not the > same as yours. I know you feel differently but please realize that the term 'function', to mean any and every type of callable in C++, is not a
universally agreed on terminology. I would bet that for the vast majority of C++ programmers a function is:
ReturnType FunctionName(ZeroOrMoreFunctionParameters);
Yes, which can happen at class scope or namespace scope, and it can also be templated.