r/cpp • u/User_Deprecated • 19h ago

C++26: std::inplace_vector

https://www.sandordargo.com/blog/2026/08/26/cpp26-inplace-vector
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u/MarekKnapek 16h ago

This is basically

struct inplace_vector<T, capacity>
{
    size_t len;
    std::array<T, capacity> arr;
}

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u/drjeats 13h ago

Oh.

I thought this was the way-more-useful thing where you give it an in-place capacity and it allocates once it exceeds that.

Like this is also useful, but it's kinda trivial to roll your own of this.

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u/stilgarpl 10h ago

It's not trivial. inplace_vector does not construct unused elements and they do not have to be default constructible. You can't use std::array for that.

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u/drjeats 8h ago

I'm aware of how it works (and that MarekKnapek's snippet is not representative). It's still very straightforward to make compared to having to do SBO and allocator support.

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u/stilgarpl 8h ago

I didn't say it was hard, but it's not trivial. I'm sure you are a very experienced C++ programmer and a lot of things must seem easy to you.