How to change the result of fmt.Println with a prefix argument

Question

I have the following code:

import "fmt"

func main() {
    P("1","2","3",0)
}

func P(prefix string,a ...interface{}){
    fmt.Println(prefix,a)
}

The result is:

1 [2 3 0]

But I would like to have one of the following results instead:

1 2 3 0
[1 2 3 0]

In other words: all arguments are of same importance, so no argument should be handled in a special way.

Answer 1

Evgeny's solution (changing the function signature) is best, but if you can't change the function signature for whatever reason:

func P(prefix string, a ...interface{}) {
    toPrint := []interface{}{prefix}
    toPrint = append(toPrint, a...)
    fmt.Println(toPrint...)  // 1 2 3 0
    // without the `...` you get [1 2 3 0]
}

Or you can just fmt.Printf in a loop:

func P(prefix string, a ...interface{}) {
    fmt.Print(prefix)
    for _, aa := range a {
        fmt.Printf(" %v", aa)
    }
    fmt.Println()  // for your final newline
}

Of course the even better solution involves removing all doubt about the type you're passing in. interface{} means nothing -- define a type and stick with it!