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

On Wednesday, March 9, 2016 at 2:13:54 AM UTC-6, work wrote:

On 2016-03-09 18:34, paul Fultz wrote:

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On Tuesday, March 8, 2016 4:58 PM, Vladimir Batov javascript:> wrote:

Maybe I need a little more explanation of components in the Quick Start Guide. Perhaps, also, a comparison of writing some of the examples without using the library...

I think that's an excellent idea.

I do a comparison of something similar here: http://pfultz2.com/blog/2014/12/12/compare-overloading-2/

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... 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?

Well the bind should be unnecessary. You should be able to write: std::accumulate(v.begin(), v.end(), 0, &std::max<int>); I guess this is not the best example. In generic code, you may not know that the container is a container of ints, so by passing along `BOOST_FIT_LIFT(std::max)`, the types will be deduced. There are other cases where the types have to be deduced, because the type are either unknown to the callee or is called with different types. If it were an algorithm over tuples, not everything will be `int`, so its not as easy as writing `std::max<int>`.

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"if we construct the class as a global variable"

Should I be excited about it? Globals are often a royal pain. Do I want

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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.

Well you create function globally, and these are just functions, the same misuse that applies to functions applies here.

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.

These functions are initialized at compile-time and must be ConstCallable, so if data is added to the functions it must be initialized without side-effects, and cannot mutate the data when the function is called.

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First, by making them objects we can turn functions into first-class citizens.

Why can't I use the standard binders to achieve that?.. Or what do I gain by using Fit instead?

Bind is a simple form of lambda expressions, so you can express a lot with lambda expressions. Futhermore, the library provides the lazy adaptor which works just like std::bind with the addition of being constexpr-friendly. However, there is a lot that you can't do with bind. You can't do overloading nor recursion nor projections with bind. Even though you can do composition and partial application, there can be complications when dealing with nested bind expressions. So sometimes, its better to have a component that can just handle composition or just handle partial application. Also, bind cannot handle variadiac parameters as well.

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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 think it would be could idea to compare the library to the capabilities of bind.