From: sabbyxtabby@... (Sabby and Tabby)
Date: 2003-11-22T21:47:12+09:00
Subject: Re: behaviour change of String#gsub(pattern) {|m| ... } for ruby 1.9/ruby2?

Austin Ziegler <austin@halostatue.ca> wrote:

>   String#gsub(pattern) { |m, md| ... }
>     yields match string and matchdata
> 
>   String#gsub(pattern) { |m| ... }
>     yields match string only
> 
> That would break the least amount of code.

Lightly tested, seems to work:

  class String
    alias _sub sub
    alias _sub! sub!

    def sub(*a, &b)
      b ? _sub(*a) {|s| b.arity == 2 ? b[s, $~] : b[s]} : _sub(*a)
    end

    def sub!(*a, &b)
      s = sub(*a, &b)
      s == self ? nil : replace(s)
    end
  end

Not portable, fragile, sometimes works:

  module Kernel
    alias _sub sub
    alias _sub! sub!

    def sub(*a, &b)
      $a, $b, $c = a, b, ""

      set_trace_func(proc {|*x|
        if x[0] == 'return'
          eval("$c.replace($_.sub(*$a, &$b))", x[4])
          set_trace_func(nil)
        end
      })

      $c
    end

    def sub!(*a, &b)
      $a, $b = a, b
      r, w = IO.pipe

      fork or return set_trace_func(proc {|*x|
        w.puts(eval("$_.sub!(*$a, &$b).inspect", x[4]))
        exit!
      })

      Process.wait
      $c = eval(r.readline) or return

      set_trace_func(proc {|*x|
        if x[0] == 'return'
          eval("$_.replace($c)", x[4])
          set_trace_func(nil)
        end
      })

      $c
    end
  end