Is there a difference between slicing and an explicit reborrow when converting Strings to &strs?

Question

Are the following two examples equivalent?

Example 1:

let x = String::new();
let y = &x[..];

Example 2:

let x =         


        

Answer 1

They are completely the same for String and Vec.

The [..] syntax results in a call to Index::index() and it's not just sugar for [0..collection.len()]. The latter would introduce the cost of bound checking. Gladly this is not the case in Rust so they both are equally fast.

---

Relevant code:

• index of String
• deref of String
• index of Vec (just returns self which triggers the deref coercion thus executes exactly the same code as just deref)
• deref of Vec