From: Justin Collins <justincollins@...>
Date: 2008-02-09T07:25:41+09:00
Subject: Re: convert String to range

Ian Whitlock wrote:
> Thomas Wieczorek wrote:
>   
>> I tried to monkey patch the Range class, but it doesn't seem to work,
>> so I patched the String class:
>>
>>     
>
> I am not sure what the rules for the request should be, but
>
> p "(1..2)".to_range     # 0..2 original request
> p "1.2 - 7.2 + 3".to_range   # 1..0
> p '"a".."c"'.to_range   # 0..0
>
> all produce things I wouldn't want.
>
> I see Justin Collins got in the eval suggestion before I
> finished looking at it.  I note that
>
> eval("1.....7")
>
> causes a syntax mistake.  Is there a way to handle syntax
> problems parallel to execution errors?
>
> Ian
>   

This is a pretty strange way to go about it, but it will work even in 
the presence of errors:

require 'thwait'

def make_range(str)
        r = nil
        thr = Thread.new do
                $SAFE = 4
                begin
                        r = eval(str)
                rescue
                end
        end

        ThreadsWait.new(thr).all_waits

        r.is_a?(Range) ? r : nil
end

p make_range("1.....7")               # nil
p make_range("(1..2)")               # 1..2
p make_range("1.2 - 7.2 + 3")    # nil
p make_range('"a".."c"')              # "a".."c"
p make_range("exit!")                 # nil
p make_range("load 'evilfile.rb'") # nil


For some reason, trying to use Thread.join will prevent the exception 
handling from working.

-Justin