英文:
Log multiple returned values in Go
问题
有没有一种惯用的方法来记录返回多个值的函数的结果?这段代码无法编译通过:
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
更新摘要(特别感谢 @rvignacio):
这是Go语法中的一个特殊情况:
func eat(args ...interface{}) {}
func eatWithSpice(spice string, args ...interface{}) {}
func main() {
eat(returnPair()) // 这个可以工作
eatWithSpice("pepper", returnPair()) // 这个不行
}
作为一个特例,如果函数或方法g的返回值的数量与另一个函数或方法f的参数数量相等,并且可以分别赋值给f的参数,则调用f(g(parameters_of_g))将按顺序将g的返回值绑定到f的参数上。调用f除了调用g之外不能包含其他参数,而且g必须至少有一个返回值。如果f有一个最终的...参数,它将被赋予在分配了常规参数之后剩余的g的返回值。(http://golang.org/ref/spec#Calls)
英文:
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)
答案1
得分: 5
你可以先给这些返回值赋值:
a, b := returnPair()
log.Printf("返回值 %d %d", a, b)
你可以在"Go函数返回多个值的示例"中看到一个例子。
直接在Println
中使用多个返回值也可以(因为它接受可变参数):
在你的情况下:play.golang.org
package main
import "log"
func returnPair() (a int, b int) {
return 42, 24
}
func main() {
log.Println(returnPair())
}
输出:
2009/11/10 23:00:00 42 24
英文:
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: <kbd>play.golang.org</kbd>
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
答案2
得分: 2
我同意VonC的方法,它更加简洁,但如果你真的想要的话,你可以受到Must()
这种函数的启发,做出类似下面这样的代码:
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()))
}
编辑:
或者更通用一些:
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()))
}
英文:
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()))
}
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