Ruby中的Undefine变量

Question

假设我正在使用irb,并输入a = 5.如何删除定义,a以便键入a返回NameError？

一些背景:后来我想这样做:

context = Proc.new{}.binding
context.eval 'a = 5'
context.eval 'undef a'  # though this doesn't work.

Answer 1

有remove_class_variable,remove_instance_variable和remove_const方法,但目前没有局部变量的等价物.

Answer 2

您可以通过减少变量存在的范围来避免取消声明变量:

def scope 
  yield
end

scope do 
  b = 1234
end

b  # undefined local variable or method `b' for main:Object

Answer 3

你总是可以通过调用一个irb子shell来"清除"irb的局部变量注册表.想想Bash shell如何处理未导出的环境变量.既然您提到了交互模式,那么这个解决方案应该可以解决这个问题.

就生产代码而言,我不想将局部变量取消定义为解决方案的一部分 - 对于那种类型的场景,键控散列可能更好.

这就是我的意思:

$ irb
irb(main):001:0> a = "a"
=> "a"
irb(main):002:0> defined? a
=> "local-variable"
irb(main):003:0> irb # step into subshell with its own locals
irb#1(main):001:0> defined? a
=> nil
irb#1(main):002:0> a
NameError: undefined local variable or method `a' for main:Object
    from /Users/dean/.irbrc:108:in `method_missing'
    from (irb#1):2
irb#1(main):003:0> exit
=> #<IRB::Irb: @context=#<IRB::Context:0x1011b48b8>, @signal_status=:IN_EVAL, @scanner=#<RubyLex:0x1011b3df0>>
irb(main):004:0> a # now we're back and a exists again
=> "a"