How do you create and use constants in Go?

Declare a constant with the const keyword. Its value is fixed when the program compiles and can never change. You can group related constants in a const ( ... ) block. Inside a group, iota starts at 0 and goes up by one on each line, which makes it the usual way to build enum-like values.

A constant without a stated type is an untyped constant, so it takes the type the context needs. That is why Pi works with both float32 and float64 values. Only values the compiler can work out, such as numbers, strings and booleans, can be constants, so a slice cannot be one.

const Pi = 3.14159
const MaxUsers = 100

// Grouped constants
const (
    StatusOK     = 200
    StatusError  = 500
    StatusPending = 202
)

// iota for auto-incrementing constants
const (
    Sunday = iota  // 0
    Monday         // 1
    Tuesday        // 2
)