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Values

A value binding names a value. let makes one that never changes, and var one you can set again:

let fixedNumber = 10
let fixedText = "the quick brown fox"
var value = 10
value = 20

Types​

A binding's type comes from its value, so fixedNumber above is an i32 and fixedText a string. You can write the type yourself, after a colon:

let small : u8 = 200
let ratio : f32 = 0.5

A bare whole number is an i32 and a bare decimal an f64, unless the type you write says otherwise. A number that doesn't fit its type is refused. Types has the full list.

Assignment​

= sets a var, a field or an array's element again. It's a statement, standing on its own line, rather than an expression with a value of its own:

var total = 0
total = total + 5
total += 5

+=, -=, *=, /= and %= are shorthand for doing the arithmetic and assigning the result.

A block as a value​

A block computes a value with return, and its own bindings stay inside it:

let area = {
  let width = 6
  let height = 7

  return width * height
}