Ruby 实例评估

Question

class Setter
    attr_accessor :foo

    def initialize
        @foo = "It aint easy being cheesy!"
    end

    def set
        self.instance_eval { yield if block_given? }
    end
end

options = Setter.new

# Works
options.instance_eval do
    p foo
end

# Fails
options.set do
    p foo
end

为什么“设置”方法会失败？

编辑

想通了...

def set
    self.instance_eval { yield if block_given? }
end

需要:

def set(&blk)
    instance_eval(&blk)
end

Answer 1

是的 - yield 在定义它的上下文中计算。

写得好here , 但一个简单的例子说明了问题:

>> foo = "wrong foo"
>> options.set do
?>     p foo
>> end
"wrong foo"