How to make a vector of received size?

Question

I have a vector datawith an unknown size at compile time. I want to create a new vector of exact size. These options do not work:

let size = data.len();

let mut try1: Vec<u32> = vec![0 .. size]; //ah, you need compile-time constant
let mut try2: Vec<u32> = Vec::new(size); //ah, there is no constructors with arguments

I'm a little upset - in the Rust API, book, link or rustbyexample.com there is no information on how to make such a simple basic task with a vector. This solution works, but I don’t think it’s good to do it, it’s strange to create elements one by one, and I don’t need any exact values ​​for the elements:

let mut temp: Vec<u32> = range(0u32, data.len() as u32).collect();

Answer 1

You can use the constructor Vec::with_capacity()followed by an unsafe call set_len():

let n = 128;
let v: Vec<u32> = Vec::with_capacity(n);
unsafe { v.set_len(n); }
v[12] = 64;  // won't panic

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Answer 2

- . , , ; [0, 1, 2, …, size - 1], :

let x = (0..size).collect::<Vec<_>>();

(range(0, size) (0..size), range .)

, :

let x = std::iter::repeat(0).take(size).collect::<Vec<_>>();

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