英文:
Golang : Variable argument
问题
当我编译以下程序时：
func myPrint(v ...interface{}) {
fmt.Println("Hello", v...)
}
func main() {
myPrint("new", "world")
}
我得到一个编译错误：
调用 fmt.Println 时参数过多
我以为 v... 会展开成第二个和第三个参数，然后 fmt.Println 会看到一个包含三个项目的可变参数列表。我以为这等同于：
fmt.Println("Hello", "new", "world")
为什么会出现错误？
英文:
When I compile the following program
func myPrint(v ...interface{}) {
fmt.Println("Hello", v...)
}
func main() {
myPrint("new", "world")
}
I get a compilation error
too many arguments in call to fmt.Println
I thought v... is going to expand into 2nd, 3rd arguments and the fmt.Println would see three item variadic argument list. I thought it would be equivalent to
fmt.Println("Hello", "new", "world")
Why is it giving an error.
答案1
得分: 6
试试这个。它在可变参数前面添加了"Hello"，然后使用println一次性打印它们。
package main
import "fmt"
func myPrint(v ...interface{}) {
a := append([]interface{}{"Hello"}, v...) // 在可变参数前面添加"Hello"
fmt.Println(a...) // 一次性打印全部内容
}
func main() {
myPrint("new", "world")
}
英文:
Try this. It prepends Hello to the variadic arguments, then prints them all at once with println.
package main
import "fmt"
func myPrint(v ...interface{}) {
a := append([]interface{}{"Hello"}, v...) // prepend "Hello" to variadics
fmt.Println(a...) // println the whole lot
}
func main() {
myPrint("new", "world")
}
答案2
得分: 2
你在调用fmt.Println()时误用了可变参数的简写方式。实际上，你发送的是两个参数：一个字符串，然后是展开的interface{}类型的切片。函数调用不会将它们连接成一个单独的切片。
以下是可以编译和运行，并得到你期望结果的设计：
func myPrint(v ...interface{}) {
fmt.Print("Hello ")
fmt.Println(v...)
}
func main() {
myPrint("new", "world")
}
英文:
You're mis-using the variadic shorthand in your call to fmt.Println(). What you're actually sending is 2 arguments: a single string, then the slice of type interface{} expanded. The function call will not concatenate that into a single slice.
This design will compile and run with the results you're expecting:
func myPrint(v ...interface{}) {
fmt.Print("Hello ")
fmt.Println(v...)
}
func main() {
myPrint("new", "world")
}
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