boost::bind

Can anyone explain (simply!) what boost::bind does? From various things I've read it seems to be some way of simplifying operations on a vector (array). But whenever I've seen it used it's almost always used for handling sigc connections. So is it simply a way of adding things to an array so that they'll automatically get processed each time the array gets processed?

Sorry... but I've yet to see a simple explanation for it... :(

Isn't boost::bind the origins of std::bind which came with C++11?

You might well be right 2kaud - tho' that still doesn't make it any easier to understand... :(

Here's what Google says when I ask it what std::bind does :-

Quote:

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std::bind is a Standard Function Objects that acts as a Functional Adaptor i.e. it takes a function as input and returns
a new function Object as an output with with one or more of the arguments of passed function bound or rearrange.

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and that's one of the better descriptions! :cry:

Consider as a 'simple' example:

Code:

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using std:: placeholders::_1;

std::vector<int>v {1,2,3,4,5,6,7,8,9};

const size_t val=std::count_if(v.begin(), v.end(),
    std::bind(std::logical_and<bool>(),
        std::bind(std::greater<int>(),_1,2),
            std::bind(std::less_equal<int>(),_1,6)));

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See https://wandbox.org/permlink/D7XjbyM0i2nslhRU

is really the same as:

Code:

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const size_t val=std::count_if(v.begin(), v.end(), [](auto x) {return x > 2 && x <= 6;});

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I never did much with std::bind (or std::bind1st or std::bind2nd which came previously) - when I needed a predicate prior to C++11 I just used a functor (class with operator() defined).

PS Why do you need bind?

I've never got into using bind because you regularly see articles like this,

https://abseil.io/tips/108

This article suggest using either lambdas or absl::bind_front instead, the latter probably written by the article author.

But I note that there is an std::bind_front also,

https://en.cppreference.com/w/cpp/ut...nal/bind_front

and there it is stated that it is intended as a replacement for std::bind.

Quote:

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But I note that there is an std::bind_front also,

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For C++20. Currently implemented in GCC 9 and VS2019 16.5 - but not yet Clang.

For info about the proposal, see http://www.open-std.org/jtc1/sc22/wg...8/p0356r5.html

Quote:

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Originally Posted by 2kaud

Consider as a 'simple' example:

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Haha - that's exactly what puzzles me... bind doesn't seem to simplify things at all - it seems to make everything a lot more complicated!

Quote:

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Originally Posted by 2kaud

PS Why do you need bind?

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Many years ago I helped develop a DAW product called Harrison Mixbus though I don't have much involvement these days. However, they just asked me to get involved again so I've been taking a look at the code - which is full of boost::bind now... :cry:

Quote:

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Originally Posted by wolle

I've never got into using bind because you regularly see articles like this,

https://abseil.io/tips/108

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That's a good article wolle - thanks for finding it.

I must admit though... I still don't understand what bind does (that's useful...) :confused:

This may help https://www.geeksforgeeks.org/bind-f...laceholders-c/

Quote:

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Originally Posted by John E

I must admit though... I still don't understand what bind does (that's useful...) :confused:

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Maybe it is a question of programming style. Traditionally in procedural programming, if you don't have all parameters immediately available to call a function you gather them by asking around for them and then you call the function. In object oriented programming and, I think, in functional programming you avoid to "pull data" in this way. Instead you "push requests" to get others to do things for you. In such designs it may feel more natural to pass around a function and allow others to partially evaluate it for you by binding the parameters they have naturally available.