How can I use Go append with two []byte slices or arrays?
The Go Programming Language Specification
Appending to and copying slices
The variadic function
append
appends zero or more valuesx
tos
of typeS
, which must be a slice type, and returns the resulting slice, also of typeS
. The valuesx
are passed to a parameter of type...T
whereT
is the element type ofS
and the respective parameter passing rules apply.
append(s S, x ...T) S // T is the element type of S
Passing arguments to
...
parametersIf the final argument is assignable to a slice type
[]T
, it may be passed unchanged as the value for a...T
parameter if the argument is followed by...
.
You need to use []T...
for the final argument.
For your example, with the final argument slice type []byte
, the argument is followed by ...
,
package main
import "fmt"
func main() {
one := make([]byte, 2)
two := make([]byte, 2)
one[0] = 0x00
one[1] = 0x01
two[0] = 0x02
two[1] = 0x03
fmt.Println(append(one[:], two[:]...))
three := []byte{0, 1}
four := []byte{2, 3}
five := append(three, four...)
fmt.Println(five)
}
Playground: https://play.golang.org/p/2jjXDc8_SWT
Output:
[0 1 2 3]
[0 1 2 3]
append()
takes a slice of type []T
, and then a variable number of values of the type of the slice member T
. In other words, if you pass a []uint8
as the slice to append()
then it wants every subsequent argument to be a uint8
.
The solution to this is to use the slice...
syntax for passing a slice in place of a varargs argument. Your code should look like
log.Printf("%X", append(one[:], two[:]...))
and
five:=append(three, four...)