Instance eval in 1.8 and 1.9
in [Ruby]
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From: Gavin Sinclair on 17 Jul 2010 11:25 Hi, Porting a program from 1.8 to 1.9, I hit a stumbling block in the use of instance_eval. The following code works in 1.8 but not 1.9. instance_eval in 1.9 does not allow you to use a lambda as a block. The solution is to use a proc instead. I understand that lambdas are like methods and procs are like blocks, but what gets me is the incredibly unhelpful error message. Anyway, the code (can also see it at http://gist.github.com/479572 ) class InstanceEval def initialize(x) @block = x @context = Object.new end def run code = @block result = @object.instance_eval(&code) "* run --> #{result.inspect}" end end p = proc { :p } l = lambda { :l } # (line 16 -- for the error message below) puts InstanceEval.new(p).run puts InstanceEval.new(l).run The output in 1.8: * run --> :p * run --> :l The output in 1.9: * run --> :p code.rb:16:in `block in <main>': wrong number of arguments (1 for 0) (ArgumentError) from code.rb:10:in `instance_eval' from code.rb:10:in `run' from code.rb:19:in `<main>' To what method have I passed one argument where zero arguments were expected? Is the average Ruby programmer supposed to know that instance_eval can't take a lambda in Ruby 1.9? Perhaps it should say so in the documentation. (http://bit.ly/96HBeb) Is there a good reason ( instance_eval &lambda_object ) can't work? Thanks for any light you can shed on it. Gavin
From: Stefano Crocco on 17 Jul 2010 12:09 On Saturday 17 July 2010, Gavin Sinclair wrote: > |Hi, > | > |Porting a program from 1.8 to 1.9, I hit a stumbling block in the use > |of instance_eval. > | > |The following code works in 1.8 but not 1.9. instance_eval in 1.9 > |does not allow you to use a lambda as a block. The solution is to use > |a proc instead. I understand that lambdas are like methods and procs > |are like blocks, but what gets me is the incredibly unhelpful error > |message. > | > |Anyway, the code (can also see it at http://gist.github.com/479572 ) > | > | class InstanceEval > | def initialize(x) > | @block = x > | @context = Object.new > | end > | > | def run > | code = @block > | result = @object.instance_eval(&code) > | "* run --> #{result.inspect}" > | end > | end > | > | p = proc { :p } > | l = lambda { :l } # (line 16 -- for the error message > |below) > | > | puts InstanceEval.new(p).run > | puts InstanceEval.new(l).run > | > | > |The output in 1.8: > | > | * run --> :p > | * run --> :l > | > |The output in 1.9: > | > | * run --> :p > | code.rb:16:in `block in <main>': wrong number of arguments (1 for 0) > |(ArgumentError) > | from code.rb:10:in `instance_eval' > | from code.rb:10:in `run' > | from code.rb:19:in `<main>' > | > |To what method have I passed one argument where zero arguments were > |expected? > | > |Is the average Ruby programmer supposed to know that instance_eval > |can't take a lambda in Ruby 1.9? Perhaps it should say so in the > |documentation. (http://bit.ly/96HBeb) > | > |Is there a good reason ( instance_eval &lambda_object ) can't work? > | > |Thanks for any light you can shed on it. > | > |Gavin Your code runs without errors for me with ruby 1.9.1-p376. Stefano
From: Gavin Sinclair on 17 Jul 2010 12:57 > > Your code runs without errors for me with ruby 1.9.1-p376. > > Stefano Thanks for testing it. I should have specified my version, of course: ruby 1.9.2dev (2010-07-02 revision 28524) [i386-cygwin] Gavin
From: Caleb Clausen on 17 Jul 2010 14:30 On 7/17/10, Gavin Sinclair <gsinclair(a)gmail.com> wrote: >> >> Your code runs without errors for me with ruby 1.9.1-p376. >> >> Stefano > > Thanks for testing it. I should have specified my version, of course: > > ruby 1.9.2dev (2010-07-02 revision 28524) [i386-cygwin] It seems like this could be a regression. The error message at the very least is a bug. I suggest you file a bug report for this.
From: Brian Candler on 19 Jul 2010 09:09
Caleb Clausen wrote: > On 7/17/10, Gavin Sinclair <gsinclair(a)gmail.com> wrote: >>> >>> Your code runs without errors for me with ruby 1.9.1-p376. >>> >>> Stefano >> >> Thanks for testing it. I should have specified my version, of course: >> >> ruby 1.9.2dev (2010-07-02 revision 28524) [i386-cygwin] > > It seems like this could be a regression. Seconded. The program works OK for me with ruby 1.9.2dev (2009-07-18 trunk 24186) [i686-linux] -- Posted via http://www.ruby-forum.com/. |