On 3/10/2016 7:50 PM, Paul Fultz II wrote:
On Thursday, March 10, 2016 at 5:26:38 PM UTC-6, Edward Diener wrote:
On 3/10/2016 1:46 PM, Paul Fultz II wrote:
On Thursday, March 10, 2016 at 12:34:26 AM UTC-6, Vicente J. Botet
wrote:
Le 10/03/2016 01:12, Paul Fultz II a écrit :
On Wednesday, March 9, 2016 at 8:50:01 AM UTC-6, Zach Laine wrote:
There are a number of adaptors that I find have obscure names:
by() is a projection; why not call it project()?
I chose `by` because of how it is used linguistically. That is you
write:
`sort(v.begin(), v.end(), by(&Employee::Name, _<_))` which I read "sort by employee name". Also, if I write `by(decay, constructstd::tuple())`,
I
read "construct tuple by decay". In haskell, it uses `on` for this adaptor, which is what I originally called it. `project` is a more straighforward name. `by` is a comparator while `projet` is a projection.
By is a projection in the example of `construct`.
compress() is defined in terms of "fold", with a link to the Wikipedia page for same; why not call it foldl()? Similarly, reverse_compress()
should
be foldr().
Not `foldr`. This is because `foldr` is symetrical. For example, `foldl` and `foldr` should produce the same results:
foldl(_+_, std::string())("Hello", "-", "world"); // "Hello-world" foldr(_+_, std::string())("Hello", "-", "world"); // "Hello-world" It would be good to use a binary function that has two different types to see the difference in behavior.
Yes, you could do `flip(_+_)` to get the same effect. However, I want the callback to be consistent with compress reverse_compress, so it always is called with f(state, element). Also, `fold` and `reverse_fold` are commonly used names in C++, so I would like to keep it more consistent with those usage. If the user wants `fold_right`, it can be easily written, like
`auto fold_right = compose(compress, flip)`.
However, compress and reverse_compress work like this:
compress(_+_, std::string())("Hello", "-", "world"); // "Hello-world" reverse_compress(_+_, std::string())("Hello", "-", "world"); // "world-Hello"
I was reluctant to call it `fold` as it seems to imply some data structure to fold over, whereas this is simply an adaptor. I used the word compress as its a another name used for fold. However, it seems more people would
to
use `fold` and `reverse_fold`. You are folding the parameter pack. I like those. and I would like also fold_left, fold_right.
flow() is a super obscure name! Why is this not reverse_compose() or similar?
I actually got the name from underscore.js. The reason why I chose this name instead of `reverse_compose` is because when this is used with pipable functions it seems confusing:
reverse_compose( filter([](int i) { return i < 3; }), transfrom([](int i) { return i*i; }) )(numbers);
With the word 'reverse' there, it almost looks as if it computes the pipeline in reverse order, which it doesn't. So I would prefer a name without reverse in it. Would pipe works better?
pipe could work, I don't know how others feel about such a name.
indirect() could more easily be understood if it were called deref()
or
dereference().
Well, `indirect` is how it is commonly called in libraries such as Boost.Range, range-v3, and PStade libraries. So I would like to keep
Escriba this: prefer the
name consistent with other similar constructs.
Could you tell us what indirect is in range-v3, what is the signature and the semantics. I don't see it is used for the same purposes, but maybe I'm wrong.
It dereferences the values in a range. They both are functors that will dereference the parametrized type.
ref(flv) is a callable that wraps an lv indirect(ptr) is a callable that wraps a ptr and deref it before calling
Well, it can be used with anything that is dereferenceable. So it works with boost::optional as well.
deref/dereference will only relate the dereference action, but not the call.
deref_on_call is too long?
Yes it is.
I don't feel as strongly about partial(), but I think it might be clearer if it were called partial_apply() or curry().
Hmm, I don't think a name with `apply` in it is good name for an adaptor. Maybe you could explain why curry is not a good name here? What is the difference between partial an currying a function.
conditional() should be called invoke_first(), call_first_of(), or similar. I find it too easy to confuse with if_().
I agree conditional is not a good name.
I see, I was trying to describe an adaptor where you could put functions with conditions in it. Other people, seem to prefer a name like `linear`, so I might use that instead. This function is related to match. The difference is that one select the best matching overload and those must be exclusive and the other the first matching overload and the match can be inclusive. I would like to see the semantics on the name, but I have not a concrete proposal.
We need to take in account that this is an adaptor, so there is no call, so `invoke_first` or call_first_off will not work. Those functions creates another function object that applies a different algorithm to select the overloaded functions when called.
I've used overload -> match first_overload -> conditional
I would prefer `match` and `linear`.
I prefer those, but I'm not yet happy with. Naming is difficult.
* Documentation
The Quick Start section is good at showing a compelling motivating
case
for using the library. The result at the end of the section looks like a very good start on a "Scrap Your Boilerplate" solution for simple, dump-style printing. It's relatively easy to read and write.
The documentation is what needs the most work, from what I've seen. The Quick Start is quite nice, but then there are some things that are underexplained in the subsequent Overview and Basic Concepts sections. For instance, why are these macros used everywhere and what do they do? They should be used for the first time after showing what the expanded code looks like.
I don't think the docs should show the expansion of the macros, that is part of the implementation and not interface. I could show an "idea" what is is expanding to, with explanation of what else it is doing beyond the simple explanation. I agree hat it is absolutely needed to show the exact expansion, but it is clear that the user wants to know what is behind the scenes.
I strongly disagree. Documentation is about documenting the interface, not the implementation. Mainly because the implementation could change or vary between platforms while the interface would remain the same. If the user wants to know about the implementation, they can look at the source code or in the case of macros, look at the preprocessed output.
This will justify their use for those users that want them, and show those that don't
they can write instead.
I could show an alternative without the macros, but I would prefer to
what put
that in the Advance section. In the introduction of the library, I would rather show the constructs that can be easily used without a need to explain a bunch of caveats. I will put all of them in the advanced section. I would no mention them in the introduction as the user can create the HOF locally or use a factory.
Being able to declare the functions as global variables is a key feature of the library. The example in the quick start guide shows how to implement many things without the need for a lot of template boilerplate. For those users that prefer not to use global function objects(and I have yet seen a compelling reason not to use them) can look at the 'Advanced' section.
I realize now, that I need to spend more discussing the advantages of using global function objects(more composability), and address some of the misperceived issues with these global function objects(they can be in a namespace to avoid name conflicts and are not mutable so it won't be a problem in mutilthreaded environments).
You do need to explain why "global variables" is a key feature of the library. I cannot understand from your docs why there is any disadvantage instantiating Callables locally as opposed to globally other than the usual fact that a local object can go out of scope.
We can define functions by simply composing other functions together and we don't need to write awkward syntax nor template boilerplate for it. For example, we can simply write `make_tuple` like this:
BOOST_FIT_STATIC_FUNCTION(make_tuple) = by(decay, constructstd::tuple());
What is the type of by(decay,constructstd::tuple()) ? I thought I would be able to write locally: auto make_tuple(by(decay,constructstd::tuple())); but evidently you are saying that does not work.
Alternatively, you could write a factory function for this instead:
constexpr auto make_tuple() { return by(decay, constructstd::tuple()); }
Of course this requires the user to write `make_tuple()(xs...)`, which I don't think any user would expect this, especially since `std::make_tuple` doesn't work like that. So instead, it can be wrapped in a template function:
template
constexpr auto make_tuple(Ts&&... xs) -> declype(by(decay, constructstd::tuple())(std::forward<Ts>(xs)...)) { return by(decay, constructstd::tuple())(std::forward<Ts>(xs)...); } Which is a lot of boilerplate to compose some simple functions.
If there really is some other reason it is completely lost to me. If you would like to point to me in your doc where you explain the use of "global variables" as being a key feature of your library or as being necessary to use the functionality of your library, I would be glad to read about it and ask further about it here.
It is not a necessary feature, but it is an important feature nonetheless, and I need to spend more time explaining its usefulness.
If, OTOH, it is just your preference to use global objects as opposed to the various forms of local instantiation, I really wish you would just say that rather than acting like your library does not work correctly somehow other than with global variables.
The composability of the adaptors and functions applies to both global and local functions. The adaptors provide a simple way to create functions to be passed locally, such as creating a comparator for std::sort(ie `std::sort(first, last, by(&employee::name, _<_))`). However, they can also be used to define global/free functions in a much simpler way as well(such as writing `std::make_tuple`), which I think is equally important.
Furthermore, in a quick start guide or introduction, I want to be able to demonstrate the capabilities of the library in a way to show its usefulness, and why someone would choose to use this library. Perhaps, you are ok with awkward syntax or template boilerplate in writing your functions, and would prefer to only use the adaptors for local functions. However, there are others who will find writing global function objects with the adaptors very useful, so I want to be able to show those capabilities in the introduction of the library. I do, however, need to discuss some of the misperceived issues with using global function objects in the documentation. As the issues raised in the review were:
1) Namespacing - This is not a problem because all global function objects can be placed in a namespace.
2) Global state - This is not a problem either, because `BOOST_FIT_STATIC_FUNCTION` declares the function object const with constexpr. So there can be no mutable or changing state internally in the object, and it must be constructed without side effects.
I think addressing these concerns in the documentation will help put users at ease when using global function objects, so they have no problem taking advantage of the adaptors to build function objects globally.
Maybe I have missed something but I have the intuition that many others have missed it likewise, from the responses of others about this issue.
I agree with your intuition, and I believe the documentation should spend more time discussing these issues. I hope my email has made it somewhat clearer to you.