I’m learning rust using the rustlings, however I am not able to understand this issue: How can I initialize new Vector using the vec! macro and automatically fill it up with values from exiting 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?
What do I want?: I want to initialize new vector using the vec! macro and in the same line fill it with values from the a array values.
>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 annoation 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];