How to best implement an iterator

Go has a built-in range loop for iterating over slices, arrays, strings, maps and channels. See 4 basic range loop (for-each) patterns.

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

More code examples

Go blueprints: code for com­mon tasks is a collection of handy code examples.

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