From: dblack@...
Date: 2006-09-01T19:35:01+09:00
Subject: Re: Legal syntax, bug or what?

Hi --

On Fri, 1 Sep 2006, Jonathan Maasland wrote:

> Hi all,
>
> I'm still working on Ripper and during my explorations I came across a line 
> of code in mkmf.rb that I can't wrap my head around.
>
> Line 1313
> ---
>   opts = $arg_config.collect {|t, n| "\t#{t}#{"=#{n}" if n}\n"}
> ---
>
> When I copy-paste the entire method to a file and run it through Ruby 
> everything is fine.
> However irb doesn't accept the method:
> ----
> irb(main):001:0> def mkmf_failed(path)
> irb(main):002:1>   unless $makefile_created or File.exist?("Makefile")
> irb(main):003:2>     opts = $arg_config.collect {|t, n| "\t#{t}#{"=#{n}" if 
> n}\n"}
> irb(main):004:3*     abort "*** #{path} failed ***\n" + FailedMessage + 
> opts.join
> irb(main):005:3>   end
> irb(main):006:2> end
> irb(main):007:1>
> ------
> As you can see irb doesn't detect the end of the third line.
>
> After taking the statement apart and simplifying it, it all boils down to the 
> following construction:
> #{"=#{n}" if n}
> inside the ""main"" double-quoted string.
>
> Why does ruby accept this construct while irb doesn't?
> Doesn't Ruby see the first double-quote as the end of the string?
>
> Any clarification would be greatly appreciated.

Nested #{} are allowed, so this is some kind of irb parsing glitch.
It seems to be the = that's confusing irb for some reason:

irb(main):002:0>  "#{"hello#{}"}"
=> "hello"
irb(main):003:0>  "#{"hello=#{}"}"
irb(main):004:0*

I believe it's causing the second # to be interpreted as introducing a
comment.


David

-- 
                   David A. Black | dblack@wobblini.net
Author of "Ruby for Rails"   [1] | Ruby/Rails training & consultancy [3]
DABlog (DAB's Weblog)        [2] | Co-director, Ruby Central, Inc.   [4]
[1] http://www.manning.com/black | [3] http://www.rubypowerandlight.com
[2] http://dablog.rubypal.com    | [4] http://www.rubycentral.org