Log multiple returned values in Go
-
21-12-2019 - |
Question
Is there an idiomatic way to log result of a function returning multiple values? This won't compile:
import "log"
func returnPair() (int,int) {
return 42, 24
}
func main() {
log.Printf("Returned %v", returnPair())
}
prog.go:7: multiple-value returnPair() in single-value context
UPD summary (special thanks to @rvignacio):
This is a peculiarity in Go syntax:
func eat(args ...interface{}) {}
func eatWithSpice(spice string, args ...interface{}) {}
func main() {
eat(returnPair()) // this works
eatWithSpice("pepper", returnPair()) // this does not
}
As a special case, if the return values of a function or method g are equal in number and individually assignable to the parameters of another function or method f, then the call f(g(parameters_of_g)) will invoke f after binding the return values of g to the parameters of f in order. The call of f must contain no parameters other than the call of g, and g must have at least one return value. If f has a final ... parameter, it is assigned the return values of g that remain after assignment of regular parameters. (http://golang.org/ref/spec#Calls)
Solution
You can assign those returning values first:
a, b := returnPair()
log.Printf("Returned %d %d", a, b
You can see an example in "Multiple return values from Go functions".
Using a multiple returning value directly in Println
works though (since it accepts variadic parameters):
In your case: play.golang.org
package main
import "log"
func returnPair() (a int, b int) {
return 42, 24
}
func main() {
log.Println(returnPair())
}
Output:
2009/11/10 23:00:00 42 24
OTHER TIPS
I aprrove the method of VonC, which is cleaner, but if you really want, you can get inspired by the Must()
kind of function and do something like this:
http://play.golang.org/p/_dik4rSFBC
package main
import "fmt"
func returnPair() (int, int) {
return 42, 24
}
func displayPair(a, b interface{}) string {
return fmt.Sprint(a, b)
}
func main() {
fmt.Printf("pair: %v\n", displayPair(returnPair()))
}
EDIT:
Or more generic:
http://play.golang.org/p/DjPur-aatt
package main
import "fmt"
func returnPair() (int, int) {
return 42, 24
}
func returnTriple() (int, int, int) {
return 42, 24, 10
}
func displayPair(elem ...interface{}) string {
return fmt.Sprint(elem...)
}
func main() {
fmt.Printf("pair: %v, triple %v\n", displayPair(returnPair()), displayPair(returnTriple()))
}