Re: Issue using Ruby1.9 (instance_eval in /lib/rack/builder.rb)

[Magnus Holm <judofyr@gmail.com>]

Also see http://coderrr.wordpress.com/2009/06/02/fixing-constant-lookup-in-dsls-in-ruby-1-9/

//Magnus Holm



On Tue, Sep 15, 2009 at 13:50, Iñaki Baz Castillo <ibc@aliax.net> wrote:
>
> Using Ruby1.9 there is an issue related to instance_eval() method
> which behaves different than in 1.8. Let me show this example:
>
> --------myapp.rb------------------------
> class MyRack
>
>    MY_VAR = "helloooo"
>
>    def self.create
>        Rack::Builder.new do
>            map "/" do
>                puts "[1] MY_VAR = #{MY_VAR}"   <----- [1]  (line 20)
>                run Proc.new { |env|
>                    puts "[2] MY_VAR = #{MY_VAR}"   <----- [2]  (line 22)
>                    [ 200, {"Content-Type" => "text/plain"}, ["Yeah"] ]
>                }
>            end
>        end
>    end
>
> end
>
>
> rack_core = MyRack.create
>
> Rack::Handler::Thin.run rack_core
> ----------------------------------------
>
>
> This works great in Ruby1.8.
>
> However, in Ruby1.9 I get this error:
>
>
> /myapp.rb:20:in `block (2 levels) in core': uninitialized constant
> Rack::Builder::MY_VAR (NameError)
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `instance_eval'
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `initialize'
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:46:in
> `new'
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:46:in
> `map'
>        from /root/svn_local_copies/OpenXDMS/trunk/lib/rack/core.rb:41:in
> `block in core'
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `instance_eval'
>        from /usr/local/lib/ruby1.9/gems/1.9.1/gems/rack-1.0.0/lib/rack/builder.rb:29:in
> `initialize'
>
>
>
> If I remove line 20, then it would in runtime in line 22 (when "run"
> is invoked for a incoming request).
>
>
> The only solution for it to work in 1.9 is to add ALL the Module/Class
> namespace for ALL the modules/classes:
>
>        Rack::Builder.new do
>            map "/" do
>                puts "[1] MY_VAR = #{::MyRack::MY_VAR}"   <----- [1]  (line 20)
>                run Proc.new { |env|
>                    puts "[2] MY_VAR = #{::MyRack::MY_VAR}"   <-----
> [2]  (line 22)
>                    [ 200, {"Content-Type" => "text/plain"}, ["Yeah"] ]
>                }
>            end
>        end
>
>
> It's VERY important to note that if I use "MyRack::MY_VAR" instead of
> "::MyRack::MY_VAR" then it would *also* fail in Ruby1.9:
>
>    `block (2 levels) in core': uninitialized constant
> Rack::Builder::MyRack (NameError)
>
>
> It seems that using instance_eval in Ruby1.9 a class/module is just
> looked for into the class/module executing the instance_eval and
> doesn't look on top of it.
>
>
> Regards.
>
>
> --
> Iñaki Baz Castillo
> <ibc@aliax.net>
>