In golang is there a nice way of getting a slice of values from a map?

Question

If I have a map m is there a better way of getting a slice of the values v then

package main
import (
  \"fmt\"
)

func main() {
    m := make(map[int]string         


        

Answer 1

As far as I'm currently aware, go doesn't have a way method for concatenation of strings/bytes in to a resulting string without making at least /two/ copies.

You currently have to grow a []byte since all string values are const, THEN you have to use the string builtin to have the language create a 'blessed' string object, which it will copy the buffer for since something somewhere could have a reference to the address backing the []byte.

If a []byte is suitable then you can gain a very slight lead over the bytes.Join function by making one allocation and doing the copy calls your self.

package main
import (
  "fmt"
)

func main() {
m := make(map[int]string)

m[1] = "a" ;    m[2] = "b" ;     m[3] = "c" ;    m[4] = "d"

ip := 0

/* If the elements of m are not all of fixed length you must use a method like this;
 * in that case also consider:
 * bytes.Join() and/or
 * strings.Join()
 * They are likely preferable for maintainability over small performance change.

for _, v := range m {
    ip += len(v)
}
*/

ip = len(m) * 1 // length of elements in m
r := make([]byte, ip, ip)
ip = 0
for  _, v := range m {
   ip += copy(r[ip:], v)
}

// r (return value) is currently a []byte, it mostly differs from 'string'
// in that it can be grown and has a different default fmt method.

fmt.Printf("%s\n", r)
}