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Bug #8982

NoMethodError#message produces surprising output when #inspect is defined on an anonymous class

Added by myronmarston (Myron Marston) almost 7 years ago. Updated 11 months ago.

Status:
Closed
Priority:
Normal
Assignee:
-
Target version:
-
ruby -v:
ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.4.0]
Backport:
[ruby-core:57629]

Description

=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
"#"
end

raise_no_method_error_for_anonymous_class_with_inspect do
""
end

raise_no_method_error_for_anonymous_class_with_inspect do
"#"
end

raise_no_method_error_for_anonymous_class_with_inspect do
"#"
end

It produces the following output:

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

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

#inspect output: # (65 chars)
undefined method `undefined_method' for #

#inspect output: # (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 (Charlie Somerville) was kind enough to point me to the code that's the source of this issue:

(())

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

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