为什么索引 Vec 会返回一个值而不是 Index 所承诺的引用？

Question

The documentation for the Index trait says that the .index() method returns a reference to the Output associated type ( link ):

fn index(&self, index: Idx) -> &Self::Output;

For Vec<T> and the usize index, Output is T . So, I expect the variable a in the following snippet to have the type &i32 .

let v = vec![0];
let a = v[0];

However, the type of a is i32 . Why? I am learning Rust and, as far as I understand, Rust requires you to be explicit everywhere and never performs value<->reference conversions implicitly. Hence the question.

Answer 1

There's an automatic dereference added when the brackets are de-sugared. The std::ops::Index documentation says, " container[index] is actually syntactic sugar for *container.index(index) ."