Bug #10194: OpenStruct does not throw an exception when calling missing method with no arguments.

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.1.2p95 (2014-05-08 revision 45877) [x86_64-linux]
• Backport: 2.0.0: UNKNOWN, 2.1: UNKNOWN

[[e-mail] (Alex Pogrebnyak)]

Below is the sample that shows the problem:
#!/usr/bin/env ruby

require 'ostruct'

class TestMethodMissing < OpenStruct
  def initialize ()

    super(
      { "foo" => "bar" }
    )

  end


  def main()

    self.no_such_method

    puts "BUG! Should fail on the previous line"
  end

end

TestMethodMissing.new( ).main( )

I expect when calling self.no_such_method to generate an error.

The error can be traced to ostruct.rb method_missing implementation

Here is the dump of the method with >> showing the trouble line:

def method_missing(mid, *args) # :nodoc:
  mname = mid.id2name
  len = args.length
  if mname.chomp!('=')
    if len != 1
      raise ArgumentError, "wrong number of arguments (#{len} for 1)", caller(1)
    end
    modifiable[new_ostruct_member(mname)] = args[0]
  elsif len == 0
>>    @table[mid]
  else
     err = NoMethodError.new "undefined method `#{mid}' for #{self}", mid, args
    err.set_backtrace caller(1)
    raise err
  end
end

There should be a check that @table[mid] does not return nil, and in case of nil raise an error

[marcandre (Marc-Andre Lafortune)]

• Status changed from Open to Rejected

It would have been a possible design choice to prevent calling a getter unless a member has been previously set.

I believe it is too late for this change though, as it could produce severe incompatibilities.

[avit (Andrew Vit)]

The design of OpenStruct is to allow all method calls. (It is similar to a Hash but with method access.)

You can use a regular Struct if you need strict properties, or something from the Hashie gem might do what you're looking for.

[[e-mail] (Alex Pogrebnyak)]

Thanks for mentioning Hashie gem. It does exactly what I need.