Ruby：无法从方法调用类实例

Question

我显然是Ruby的新手，并且对编程还是一个新手，非常感谢您的帮助。

这是我的代码段：

class Player
    attr_accessor :name, :hp

    def initialize(name, hp)
        @name = name
        @hp = hp
    end

    def name
        @name
    end

    def hp
        @hp
    end
end

def prompt
    print "> "
end

prompt; pname = gets.chomp
player = Player.new(pname, rand(20..30))

puts "#{player.name} \:\: #{player.hp} HP"

def test
    puts "#{player.name} \:\: #{player.hp} HP - IN METHOD"
end

test

运行时，结果如下：

$ ruby​​ wtf.rb

> Test Name

Test Name :: 20 HP

wtf.rb:24:in `test': undefined local variable or method `player' for main:Object (NameError) from wtf.rb:27:in `<main>'

为什么我的呼叫在第一种情况下起作用，但在第二种情况下却不起作用？ 是否因为它现在正在“测试”方法中寻找新的“玩家”变量？ 如果是这样，我该如何从先前创建的类实例中调用一个？

谢谢！

Answer 1

player被定义为方法test范围之外的局部变量，

将player引用更改为@player ，使其成为实例变量

这是有关范围和变量的快速参考 ，也是一个类似的问题

附带说明一下，您不应将test用作方法名称，因为它已经在Kernel上定义

irb(main):001:0> method(:test)
=> #<Method: Object(Kernel)#test>

Answer 2

def test
  puts "#{player.name} \:\: #{player.hp} HP - IN METHOD"
end

您忘记了将player传递给方法：

def test(player)
  puts "#{player.name} \:\: #{player.hp} HP - IN METHOD"
end

test(player) # => player = Player.new(pname, rand(20..30)) :: 22 HP - IN METHOD

Answer 3

Ruby没有像Javascript这样的函数的方法的词法作用域，因此（红宝石）为：

player = Player.new(pname, rand(20..30))
def test
    # error: undefined variable or method 'player', 
    # this happens because player was defined
    # in an unrelated scope outside this method
    puts "#{player.name} \:\: #{player.hp} HP - IN METHOD"
end
test

不等同于此（javascript）

var player = new Player(pname, ...);
var test = function() {
    # works as expected, player is available because it was defined
    # in the parent scope
    console.log(player.name + "\:\:" + player.hp + " HP - IN METHOD");
};
test();

如果您想要类似于ruby的词法作用域的内容，也许您应该使用lambda

player = Player.new(pname, rand(20..30))
test = lambda do
    # works as expected, this block scope inherits from parent scope where the block
    # was created, so, it can access player local variable
    puts "#{player.name} \:\: #{player.hp} HP - IN METHOD"
end
test.call