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vectorrust

Initialize vector using vec! macro and fill it with values from existing array

How can I initialize new Vector using the vec! macro and automatically fill it up with values from an existing array? Here's the code example:

let a = [10, 20, 30, 40]; // a plain array
let v = vec![??];       // TODO: declare your vector here with the macro for vectors

What can I fill in (syntax wise) instead of the ??? characters?

Solution

  • Since Vec<T> impls From<[T; N]>, it can be created from an array by using the From::from() method or the Into::into() method:

    let v = Vec::from(a);
// Or
let v: Vec<_> = a.into(); // Sometimes you can get rid of the type 
                          // annotation if the compiler can infer it

    The vec![] macro is not intended for that; it is intended for creating Vecs from scratch, like array literals. Instead of creating an array and converting it, you could use the vec![] macro:

    let v = vec![10, 20, 30, 40];