做七周七语言ruby第二天习题的时候要实现一个简单的Tree类，以下代码可以运行，但是把
children.each {|c| c.visit_all(n+1) {|node| puts "-#{node.node_name}"}}
这行的{|node| puts "-#{node.node_name}"}改成&block就跑不起来，请问是为什么？

#!/usr/bin/ruby class Tree attr_accessor :children,:node_name def initialize(tree) tree.each do |key,value| @node_name = key @children = value.map {|(key,value)| Tree.new(key => value)} end end def visit_all(n,&block) visit &block print ' ' * n children.each {|c| c.visit_all(n+1) {|node| puts "-#{node.node_name}"}} end def visit(&block) block.call self end end ruby_tree = Tree.new({ 'grandpa' => { 'day' => {'child 1' => {},'child 2' => {}},'uncle' => {'child 3' => {},'child 4' => {}} } }) ruby_tree.visit_all(1) {|node| puts "-#{node.node_name}"}

ps: ruby环境是2.1.3