From: "alexeymuranov (Alexey Muranov)" <redmine@...>
Date: 2013-10-18T13:57:40+09:00
Subject: [ruby-core:57929] [ruby-trunk - Bug #8982] NoMethodError#message	produces surprising output when #inspect is defined on an	anonymous class


Issue #8982 has been updated by alexeymuranov (Alexey Muranov).


nobu (Nobuyoshi Nakada) wrote:

> '#' at the beginning is assumed the string is same as Object#inspect, otherwise its class name is appended since the string may not represent the class.

> If the `inspect` string is too long, just ignore it and use default conersion method

Looks like defensive programming to me.
----------------------------------------
Bug #8982: NoMethodError#message produces surprising output when #inspect is defined on an anonymous class
https://bugs.ruby-lang.org/issues/8982#change-42513

Author: myronmarston (Myron Marston)
Status: Open
Priority: Normal
Assignee: 
Category: 
Target version: 
ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]
Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN


=begin
Given the following script:

 def raise_no_method_error_for_anonymous_class_with_inspect(&block)
   klass = Class.new do
     define_method(:inspect, &block)
   end

   begin
     instance = klass.new
     puts "#inspect output: #{instance.inspect} (#{instance.inspect.length} chars)"
     instance.undefined_method
   rescue NoMethodError => e
     puts e.message
   end

   puts
 end

 raise_no_method_error_for_anonymous_class_with_inspect do
   "#<MyAnonymousClass>"
 end

 raise_no_method_error_for_anonymous_class_with_inspect do
   "<MyAnonymousClass>"
 end

 raise_no_method_error_for_anonymous_class_with_inspect do
   "#<MyAnonymousClass #{'a' * 45}>"
 end

 raise_no_method_error_for_anonymous_class_with_inspect do
   "#<MyAnonymousClass #{'a' * 46}>"
 end

It produces the following output:

 #inspect output: #<MyAnonymousClass> (19 chars)
 undefined method `undefined_method' for #<MyAnonymousClass>

 #inspect output: <MyAnonymousClass> (18 chars)
 undefined method `undefined_method' for <MyAnonymousClass>:#<Class:0x1017270e8>

 #inspect output: #<MyAnonymousClass aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa> (65 chars)
 undefined method `undefined_method' for #<MyAnonymousClass aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa>

 #inspect output: #<MyAnonymousClass aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa> (66 chars)
 undefined method `undefined_method' for #<#<Class:0x1017266e8>:0x101726698>

There are two surprising things here:

* It matters whether or not the first character in my `inspect` is a `#`.  If it's not, ruby appends the class's `#inspect` output to it.
* It matters how long my `inspect` string is.  If it's less than 66 characters, it's used; if it's more than 65, it's discarded, and the default anonymous `#inspect` is used instead.

Both of these things are extremely surprising and seem very arbitrary and inconsistent.

I brought this up on ruby parley and @charliesome was kind enough to point me to the code that's the source of this issue:

((<error.c#L1091-1104|URL:https://github.com/ruby/ruby/blob/870dc20922d1ab0b628d24e64e971e8eb77ecd61/error.c#L1091-1104>))

So it looks intentional, but I think this is a bug.
=end



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