Go: Iterator pattern

Go has built-in range loops for iterating over slices, arrays, strings, maps and channels. See Range loops explained.

To iterate over other types of data, an iterator function with callbacks is a clean and fairly efficient abstraction.

Basic iterator pattern

// Iterate calls the f function with n = 1, 2, and 3.
func Iterate(f func(n int)) {
        for i := 1; i <= 3; i++ {
                f(i)
        }
}

In use:

Iterate(func(n int) { fmt.Println(n) })

1
2
3

Iterator with break

// Iterate calls the f function with n = 1, 2, and 3.
// If f returns true, Iterate returns immediately
// skipping any remaining values.
func Iterate(f func(n int) (skip bool)) {
        for i := 1; i <= 3; i++ {
                if f(i) {
                        return
                }
        }
}

In use:

Iterate(func(n int) (skip bool) {
        fmt.Println(n)
        return n == 2
})

1
2