Type System

Run has a simple type system with the following built-in types:

Integer types

• int - platform-sized signed integer
• uint - platform-sized unsigned integer
• i32 - 32-bit signed integer
• i64 - 64-bit signed integer
• u32 - 32-bit unsigned integer
• u64 - 64-bit unsigned integer
• byte - alias for u8, a single byte

Floating point types

• f32 - 32-bit floating point number
• f64 - 64-bit floating point number

Other types

• bool - boolean value, true or false
• string - UTF-8 encoded string

Type inference

Run can infer the type of a variable from its initial value. You rarely need to write types explicitly when using short declarations.

package main

use "fmt"

pub fun main() {
    x := 42          // int
    pi := 3.14159    // f64
    name := "Run"    // string
    active := true   // bool

    fmt.println(x)
    fmt.println(pi)
    fmt.println(name)
    fmt.println(active)
}

When you need a specific numeric type, use an explicit type annotation:

let small i32 = 100
let big u64 = 1_000_000
let precise f64 = 0.1