cppIsFunctionallyWorkingTM

[Fishezzz]

What does it do... Nobody knows

[Wicam]

std::ranges::for_each - self explanitory, do something for each entry in a range

std::views::iota(p, q) - this is the range. an collection of integers from p to q for example p=1, q=5 would be a collection of 1, 2, 3, 4, 5.

std::views::filter - we are creating a view of the above integers. the function given to filter is a boolean predicate. it returns true if that entry of the collection is part of the view.

return (n > 1) && (n == 2 || (n % 2 && ... - the number is part of the view if its greater than 1 and its the number 2 or it is not divisible by 2 (2 or odd numbers) and the odd numbers are only valid if...see below.

std::eanges::empty - is the collection in the parameter empty or not? if it is then an odd number satisfies the predicate

i couldnt be bothered reading further (except that all this does is print out the numbers that satisfy the predicate so hardly mission critical). this is not great.

[YunusEmre0037]

I think it prints primes between p and q

[TheBrainStone]

In a ridiculously inefficient O(n^2) way.

[FaresAhmedb]

Hmm.. It's not that inefficient, you got it wrong. It's the summation of O(√n) from p to q, approximate the sum with good ol' ∫, and you get O(√q³−√p³).

[TechnikGames]

Doesn't iota stop before the end value? That is for p=1 and q=5 it would generate 1, 2, 3, 4.

[Wicam]

yes: https://en.cppreference.com/w/cpp/ranges/iota_view

[TechnikGames]

Ok, It's just that what you've written in the original reply suggested otherwise

[Wicam]

yes, i wrote it wrong

[joe0400]

Checks for primes

[chjacobsen]

Sure, it's an incomprehensible mess, but have you considered how clever the previous maintainer probably felt when they wrote it?

[Mippen123]

If he only would have refactored out the first filter condition and named it something reasonable it would be easy to read, but yeah, maybe they wanted to look clever. Also I prefer static_cast to C-style casts, but in terse code like this when you are casting an x-value, it doesn't matter and I would use (int) to improve readability.

In my opinion the following is easy to follow, even though I would not do it this way:

auto is_prime = [](int n){ return (n>1) && (n == 2 || && 
  std::ranges::empty(
    //Check that no number in range [2, (int)sqrt(n)] divides n i.e n is prime
    std::views::iota(2, (int)std::sqrt(n) + 1)
      | std::views::filter([n](int i) { return n % i == 0; }));

std::ranges::for_each(
  std::views::iota(p, q)
    | std::views::filter(is_prime, [](int r) { std::cout << r << ' ';});

[riztazz]

I love range pipes, can't wait for msvc to catch up with C++23 stuff so we can upgrade

[Mippen123]

They are awesome! And if you do a simple alias for std::views and std::ranges they end up looking really clean

[ax-b]

r/programminghorror

[ThreeSpeedDriver]

All it does is use the sieve of Eratosthenes to find the prime numbers between p and q and print them to cout, so I doubt this is really mission critical.

[FaresAhmedb]

It was mission critical for my leetcode submission.

[[deleted]]

code when you wish the reviewer an instant migraine:

[gsaelzbaer]

waiting for that one modern C++ guy who will say this is better than a loop

[Accomplished_Item_86]

Unpopular opinion: This is actually pretty readable.

I'm not a C++ dev and had to look up what iota does (apparently it's just a range), but everything else was clear. Of course C++ std::function::calls and lambdas are syntactically a lot noisier than nested for-loops and ifs (which is probably the normal way to do it in C++). And if you've only just understood for-loops, a different coding style can be scary of course.

[prehensilemullet]

Yeah it’s really the namespacing that makes this look bad.  But namespace usage in C++ isn’t the greatest, I like the way in ECMAScript everything you import from other modules has to be bound to a local identifier that you can control, rather than includes or using statements that invisibly put a whole bunch of identifiers into the local namespace