by kirklin.mcdonald:

Consider:

$ cat test2.go
package main

import "fmt"

func F() (int, string) {
  fmt.Printf("foo\n")
  return 0, ""
}

var x, _ = F()

func main() {}
$ 6g -o test2.6 test2.go
$ 6l -o test2 test2.6
$ ./test2
foo
foo
$ echo $GOOS $GOARCH
linux amd64
$ hg identify $GOROOT
a9db512e9a3a

Declaring the variables as "x, y" instead of "x, _" results in
"foo" being 
printed once.