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Bug #11326

Updated by nobu (Nobuyoshi Nakada) over 9 years ago

Hi, 

 yesterday I've stumbled on weird behavior defining writers as Struct members. 

 While this code works on MRI it breaks on JRuby and Rubinius: 

 ```ruby 
 Struct.new(:x=).new(nil).x = 23 
 ``` 

 On JRuby it fails with: 

 ``` 
 ArgumentError: wrong number of arguments calling `x=` (1 for 0) 
     from (irb):1:in `evaluate' 
     from org/jruby/RubyKernel.java:1111:in `eval' 
     from org/jruby/RubyKernel.java:1511:in `loop' 
     from org/jruby/RubyKernel.java:1274:in `catch' 
     from org/jruby/RubyKernel.java:1274:in `catch' 
     from /home/ps/.rvm/rubies/jruby-1.7.20/bin/irb:13:in `(root)' 
 ```  

 On Rubinius it gives: 

 ``` 
 ArgumentError: given 1, expected 0 
     from (irb):1 
     from kernel/common/block_environment.rb:53:in `call_on_instance' 
     from kernel/common/eval.rb:176:in `eval' 
     from kernel/common/kernel.rb:510:in `loop' 
     from kernel/bootstrap/proc.rb:20:in `call' 
     from kernel/common/throw_catch.rb:30:in `catch' 
     from kernel/common/throw_catch.rb:8:in `register' 
     from kernel/common/throw_catch.rb:29:in `catch' 
     from kernel/bootstrap/proc.rb:20:in `call' 
     from kernel/common/throw_catch.rb:30:in `catch' 
     from kernel/common/throw_catch.rb:8:in `register' 
     from kernel/common/throw_catch.rb:29:in `catch' 
     from /home/ps/.rvm/gems/rbx-2.5.2@global/gems/rubysl-irb-2.1.1/bin/irb:12:in `__script__' 
     from kernel/common/kernel.rb:497:in `load' 
     from /home/ps/.rvm/gems/rbx-2.5.2@global/bin/irb:23:in `__script__' 
     from kernel/delta/code_loader.rb:66:in `load_script' 
     from kernel/delta/code_loader.rb:152:in `load_script' 
     from kernel/loader.rb:655:in `script' 
     from kernel/loader.rb:809:in `main' 
 ``` 

 I've reported this as a bug to the JRuby team at https://github.com/jruby/jruby/issues/3097 

 Charles rejected it and said: 

 > ``` 
 I think I'm going to call this a bug in MRI and ask you to re-file it with them. I believe the `:x=` :x= should be kicked out as an invalid attribute name rather than defined as a write-only attribute. I believe the latter behavior is happening only accidentally because of how MRI detects that you're defining an `=` = method. 
 ``` 

 So here I am. 

 I don't have a strong opinion whether defining a writer member should be possible or not. 

 It would be nice to have one single behavior across the 3 major Ruby implementations :) 

 What do you think? 

 Kind regards, 
   Peter

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