How to use the copy function

The built-in copy function copies elements into a destination slice dst from a source slice src.

func copy(dst, src []Type) int

It returns the number of elements copied, which will be the minimum of len(dst) and len(src). The result does not depend on whether the arguments overlap.

As a special case, it’s legal to copy bytes from a string to a slice of bytes.

copy(dst []byte, src string) int


Copy from one slice to another

var s = make([]int, 3)
n := copy(s, []int{0, 1, 2, 3}) // n == 3, s == []int{0, 1, 2}

Copy from a slice to itself

s := []int{0, 1, 2}
n := copy(s, s[1:]) // n == 2, s == []int{1, 2, 2}

Copy from a string to a byte slice (special case)

var b = make([]byte, 5)
copy(b, "Hello, world!") // b == []byte("Hello")

Further reading

Slices and arrays in 6 easy steps

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