如何将变量传递给动态更新的Ruby进程

Question

p = Proc.new{ |v| puts v }
p(5) #=> 5

这很好，但如果我想"绑定"v，使其动态更新呢。例如：

p = Proc.new{ ... puts v }
v = 5
p #=> 5
v = 7
p #=> 7

Answer 1

您已经做对了。只需使用调用来执行您的proc:

irb(main):001:0> v= 42
=> 42
irb(main):002:0> p= Proc.new{ puts v }
=> #<Proc:0x422007a8@(irb):2>
irb(main):003:0> p.call
42
=> nil
irb(main):004:0> v= 43
=> 43
irb(main):005:0> p.call
43
=> nil
irb(main):006:0> 

Answer 2

在proc之前声明变量。当创建proc时，它将考虑已经声明的任何局部变量。

这是因为变量是在proc之后声明的。

1.9.3p327 :001 > p = Proc.new { puts a }
 => #<Proc:0x9b91e4c@(irb):1> 
1.9.3p327 :002 > p.call()
NameError: undefined local variable or method `a' for main:Object
    from (irb):1:in `block in irb_binding'
    from (irb):2:in `call'
    from (irb):2
    from /home/chris/.rvm/rubies/ruby-1.9.3-p327/bin/irb:16:in `<main>'
1.9.3p327 :003 > a = 1
 => 1 
1.9.3p327 :004 > p.call()
NameError: undefined local variable or method `a' for main:Object
    from (irb):1:in `block in irb_binding'
    from (irb):4:in `call'
    from (irb):4
    from /home/chris/.rvm/rubies/ruby-1.9.3-p327/bin/irb:16:in `<main>'

这适用于在proc之前声明的变量。

1.9.3p327 :001 > a = 1
 => 1 
1.9.3p327 :002 > p = Proc.new { puts a }
 => #<Proc:0x8cc2d44@(irb):2> 
1.9.3p327 :003 > p.call()
1
 => nil 
1.9.3p327 :004 > a = 2
 => 2 
1.9.3p327 :005 > p.call()
2
 => nil