Introduce postfixes to turn expressions into variables (like IntelliJ's .var).

[saiintbrisson]

Create two new postfixes: let and letm.

let:

"Hello, World!".let
let $0 = "Hello, World!";

and letm

"Hello, World!".letm
let mut $0 = "Hello, World!";

If possible, creating variables for expressions being called would be awesome:

vec![1, 2, 3].into_iter().map(|foo| foo * 2);

calling .let after vec![1, 2, 3] would turn into:

let $0 = vec![1, 2, 3];
$0.into_iter().map(|foo| foo * 2);