comparing strings.Join to concatenating strings

main.go

package test

import "strings"

func stringjoin(key, namespace string) {
	_ = strings.Join([]string{namespace, "build.", key}, "")
}

func concat(key, namespace string) {
	_ = namespace + "build." + key
}

main_test.go

package test

import "testing"

func BenchmarkStringJoin(b *testing.B) {
	for i := 0; i < b.N; i++ {
		stringjoin("hello", "world")
	}
}

func BenchmarkConcat(b *testing.B) {
	for i := 0; i < b.N; i++ {
		concat("hello", "world")
	}
}

result

$ go test -bench .
testing: warning: no tests to run
PASS
BenchmarkStringJoin	10000000	       210 ns/op
BenchmarkConcat	20000000	       109 ns/op
ok  	_/tmp/pp	4.618s

$ # including memory allocation
$ go test -bench . -benchmem
testing: warning: no tests to run
PASS
BenchmarkStringJoin	10000000	       214 ns/op	      32 B/op	       2 allocs/op
BenchmarkConcat	20000000	       110 ns/op	      16 B/op	       1 allocs/op
ok  	_/tmp/pp	4.707s