匿名go函数可以调用自身吗？

Question

I'm just running through the Tour of Go, and got to the tree walker exercise. Its obvious recursion, but closing the channel is a special case after the final pop off the call stack. Anyway, I ended up implementing it thusly:

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
    var walker func(t *tree.Tree, ch chan int)
    walker = func(t *tree.Tree, ch chan int) {
        if (t.Left != nil) {
            walker(t.Left, ch)
        }
        ch <- t.Value
        if (t.Right != nil) {
            walker(t.Right, ch)
        }
    }
    walker(t, ch)
    close(ch)
}

So far my impression of go is that they prefer to avoid saying things if they can, so the declaration of var walker before the definition seems off. Perhaps I missed some detail that would allow a function to refer to itself without the declaration? It would be a little nicer if it could be:

// Walk walks the tree t sending all values
// from the tree to the channel ch.
func Walk(t *tree.Tree, ch chan int) {
    func(t *tree.Tree, ch chan int) {
        if (t.Left != nil) {
            __me__(t.Left, ch)
        }
        ch <- t.Value
        if (t.Right != nil) {
            __me__(t.Right, ch)
        }
    }(t, ch)
    close(ch)
}

This is a simple trivia question, but I'm new enough to the language that I am not finding the answer...

Answer 1

You cannot use a variable before it is declared, and it is not yet declared inside its initialization statement.

So yes, the declaration line is required, and no, there is no way to avoid it.