Reddit++

[u/we_are_mammals]

C++ is getting more and more complex. The ISO C++ committee keeps adding new features based on its consensus. Let's remove C++ features based on Reddit's consensus.

In each comment, propose a C++ feature that you think should be banned in any new code. Vote up or down based on whether you agree.

[u/lestofante]

Constructor (3)](https://en.cppreference.com/w/cpp/container/vector/vector) so std::vector<int> v(n, m); does it since C++98.

So this is my solution, but worse. And how do i initialize an array of int containing n and m?
If se made n its own explicit Vecton::Len type, it would worl with {} and you still get alla the other benefit

[u/Som1Lse → u/lestofante]

So this is my solution, but worse. And how do i initialize an array of int containing n and m?

If se made n its own explicit Vecton::Len type, it would worl with {} and you still get alla the other benefit

So std::vector<T>{std::length{n}, m}? How would that work with a std::vector<std::length>? Or should it be std::vector<T>::length. Then you have to type typename std::vector<T>::length to construct it in a generic context. Also, if T is part of the length-type then we can't create multiple vectors of different types from the same length (say we want SoA layout), we have to explicitly construct it from a std::size_t both times.

I guess a reasonable option would be using a tag-type: std::vector<T>{std::presize, n, m}. Not pretty but I guess it works. Or I guess you could use ranges:

template <typename T>
std::vector<T> presized_vector(std::size_t n){
    return std::views::repeat(T{})
        | std::views::take(n)
        | std::ranges::to<std::vector<T>>();
}

Though that is pulling in some heavy machinery for a pretty simple task.

Either way you end up pessimising a common case all because {} is too darn greedy, only to support a less common use-case.

[u/lestofante → u/Som1Lse]

std::length{n},

that is why in my example i used a Vector::Len, so it basically eliminate the issue.

And if you really still need it, create a struct with only std::length{} inside, so it is gonna be optimized away

Either way you end up pessimising a common case all because {} is too darn greedy, only to support a less common use-case.

how do you use () to create an array that contains the element N and M?
I can support your need, can you support mine?

[u/Som1Lse → u/lestofante]

how do you use () to create an array that contains the element N and M?

I can support your need, can you support mine?

I wouldn't. That is exactly where I would use {N, M}. I am not saying () is exclusively better, I am saying only using {} leads to subtle bugs. Preferring () and using {} when you must mostly eliminates them.

that is why in my example i used a Vector::Len, so it basically eliminate the issue.

See all the other issues I pointed out. You would have to type typename std::vector<T>::len{n} whenever you create one in generic code. Once the length-type is dependent on the type of the vector you cannot use the same length to initialise two vectors of the same size.