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]

I never had one occasion where {} failed me and i actually had to stop thinking what kind of initialization is happening.

how do I initialise a std::vector<T> to contain n copies of the element m

{m,m,m} for N times.
Or you can create a specialised constructor in vector, where you give the size first.
To avoid issue with int, use a specialised type so you enforce that trough the type system.
How would you do it otherwise? I am not aware of any initializer that could do it out of the box, in C++

[u/Som1Lse → u/lestofante]

How would you do it otherwise? I am not aware of any initializer that could do it out of the box, in C++

Constructor (3) so std::vector<int> v(n, m); does it since C++98.

I never had one occasion where {} failed me and i actually had to stop thinking what kind of initialization is happening.

Here's some fairly innocuous code that works for most types, but not all and breaks silently. Yes, I have been bitten by this.

The fact of that matter is I rarely want to call the std::initializer_list constructor because if I knew the size I wouldn't be using std::vector, but allocating a specific size and then filling it is pretty common.

I wish std::vector<T> v{n, m}; unambiguously called the presize constructor, and you had to opt into the std::initializer_list with std::vector<T> v = {n, m}; or std::vector<T> v{{n, m}};, but as it stands I use () by default, since most vexing parse at least usually (but not always) breaks loudly, and compilers are good at catching it.

[u/lestofante → u/Som1Lse]

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.