Immutable Variables

Immutable variables are declared with the let keyword. They must be assigned a value and cannot be reassigned.

package main

use "fmt"

let pi f64 = 3.14159
let max_size int = 1024
let greeting string = "Hello"

pub fun main() {
    fmt.println(pi)
    fmt.println(max_size)
    fmt.println(greeting)
}

The compiler enforces immutability — any attempt to reassign a let variable is a compile-time error. The error message points to the original declaration and suggests using var if reassignment is needed. Use let when a value should never change, and var when it needs to be updated.