关闭如何为Ruby的define_singleton_method工作？

class A
    def msg
        "hello"
    end

    def p
        Proc.new { msg }
    end

    def lam
        lambda { msg }
    end

    def blk
        (1..3).map { msg }.join(" and ")
    end

    def d1(obj)
        obj.define_singleton_method(:say1) { msg }
    end

    def d2(obj)
        bound = msg # <== Why is this needed?
        obj.define_singleton_method(:say2) { bound }
    end
end

a = A.new

puts a.p.call

puts a.lam.call

puts a.blk

obj = Object.new

a.d1(obj)

begin
# Why does this fail?
puts obj.say1
rescue
puts "caught: #{$!}"
end

a.d2(obj)

puts obj.say2

产生这个输出：

hello
hello
hello and hello and hello
caught: undefined local variable or method `msg' for #<Object:0x00000001a20638>
hello

是什么让d1和d2有所不同？为什么所有的块都会看到msg,除了传递给define_singleton_method的块？

更新：

我认为归结为：

Proc bodies have a lexical scope like functions in Lisp and
JavaScript,meaning that when Ruby encounters a free variable inside a
proc body,its value is resolved within the context the proc was
defined. This is what makes closures possible. Methods are different,
however. A method’s context is the object to which they are bound.
When Ruby encounters a free variable inside a method body,it assumes
the variable refers to another method on the object,and this is what
saves us from having to prefix same-object methods with “this” or
“self”.

我在这里找到的：Of closures,methods,procs,scope,and Ruby.

具有{msg}的所有这些各种块必须像Proc主体那样工作. define_singleton_method正在获取块并为其提供方法规则.