英文:
Function declaration in Golang
问题
在Golang中，声明函数有两种不同的方式，如下所示：
package main
import "fmt"
var someFunc = func(arg string) {
fmt.Println(arg)
}
func main() {
someFunc("Hello")
}
上面的代码是可以工作的。然而，下面的代码是无法工作的：
package main
import "fmt"
var someFunc = func(arg string) {
fmt.Println(arg)
}
var main = func() {
someFunc("Hello")
}
它会报错：
runtime.main: undefined: main.main
那么func someFunc()和var someFunc = func()之间有什么区别呢？
我发现这个问题可能是因为我也写了很多JavaScript代码。在Go中，我很少看到人们像var someFunc=func()这样声明函数。在这两种方式中，我们可以说哪一种比另一种更正确吗？
英文:
It seems there are two different ways to declare a function in Golang, like this:
package main
import "fmt"
var someFunc = func(arg string) {
fmt.Println(arg)
}
func main() {
someFunc("Hello")
}
The above works. However, the below does not work:
package main
import "fmt"
var someFunc = func(arg string) {
fmt.Println(arg)
}
var main = func() {
someFunc("Hello")
}
It will complain:
runtime.main: undefined: main.main
So what's the difference between func someFunc() and var someFunc = func()?
The reason I found this is probably because of I code a lot of Javascript, too. It seems in Go, I rarely see people declaring a function like var someFunc=func(). Of these two, can we say which one is more correct than the other one?
答案1
得分: 18
当你这样写的时候：
var someFunc = func(arg string) {}
你是将一个匿名函数赋值给了 someFunc 变量。你也可以这样写：
someFunc := func(arg string) {}
另一种创建函数的方式是创建一个命名函数：
func someFunc(arg string) {}
命名函数只能在顶层声明，而匿名函数可以在任何地方声明。而且 main 有特殊的含义，在 main 包中必须有一个名为 main 的命名函数，这就是为什么你在第二种情况下会得到一个错误。
英文:
When you do
var someFunc = func(arg string) {}
you are assigning an anonymous function to the somefunc variable. You could also write it like this:
somefunc := func(arg string) {}
The other way to create a function is to create a named function:
func somefunc(arg string) {}
Named functions can only be declared at the top level whereas anonymous functions can be declared anywhere. And main has a special meaning, there has to be a named function called main in the main package, that's why you got an error in the second case.
答案2
得分: 5
主函数（main）的声明。
这是声明一个匿名函数，并将其赋值给名为 main 的变量。在Go语言中，函数是一等公民，你可以将函数本身赋值给一个变量。
英文:
func main() {
This is declaring a function named main.
var main = func() {
This is declaring an anonymous function and assigning it to a variable called main. Functions are first-class data in Go. You can assign the function itself to a variable.
答案3
得分: 4
这是一个函数声明：
func main() {}
这是一个变量声明：
var main = func() {}
语言规范中说：
> "主包必须具有包名main并声明一个不带参数且不返回值的函数main。"
变量声明不是函数声明，因此不符合main函数的要求。
英文:
This is a function declaration:
func main() {}
This is a variable declaration:
var main = func() {}
The language specification says:
> "The main package must have package name main and declare a function
> main that takes no arguments and returns no value."
A variable declaration isn't a function declaration and therefore doesn't meet the requirements for main.
答案4
得分: 0
它在抱怨，因为所有的函数都必须在主函数内部调用，而主函数是程序的起始点。
例如：
package main
import "fmt"
func Print() {
fmt.Println("Print function")
}
func main() {
Print()
}
英文:
It is complaining because all functions have to be called inside the main function which is the starting point of your program.
Ex:
package main
import "fmt"
func Print() {
fmt.Println("Print function")
}
func main() {
Print()
}
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