From: nobu@...
Date: 2017-03-28T05:44:59+00:00
Subject: [ruby-core:80421] [Ruby trunk Bug#13358] OpenStruct overriding	allocate

Issue #13358 has been updated by nobu (Nobuyoshi Nakada).


Eregon (Benoit Daloze) wrote:
> But my main issue with this fix is it only addresses a specific use-case and not the general issue:
> `#respond_to?` should work on any object, even uninitialized and just `#allocate`-d.
> `Kernel#respond_to_missing?` works on any object, but `OpenStruct#respond_to_missing?` does not currently.

I can't get your point.
`OpenStruct#respond_to?` works as others, and `OpenStruct#respond_to_missing?` too.
Anyway `Kernel#respond_to_missing?` is private and not to be used directly.

> For instance, `Class.instance_method(:allocate).bind(OpenStruct).call.respond_to?(:foo)` breaks.

Why bypass overridden methods?

> I will commit my patch tomorrow unless you object.

I object.

> It is more robust and has no significant downside.

No merit.


----------------------------------------
Bug #13358: OpenStruct overriding allocate
https://bugs.ruby-lang.org/issues/13358#change-63914

* Author: sitter (Harald Sitter)
* Status: Closed
* Priority: Normal
* Assignee: 
* Target version: 
* ruby -v: ruby 2.4.0p0 (2016-12-24 revision 57164) [x86_64-linux]
* Backport: 2.2: DONTNEED, 2.3: DONE, 2.4: DONTNEED
----------------------------------------
In https://github.com/ruby/ruby/commit/15960b37e82ba60455c480b1c23e1567255d3e05 OpenStruct gained

~~~ruby
  class << self # :nodoc:
    alias allocate new
  end
~~~

Which is rather severely conflicting with expected behavior as `Class.allocate` is meant to [not call initialize](http://ruby-doc.org/core-2.4.0/Class.html#method-i-allocate). So, in fact, the change made `allocate` of `OpenStruct` do what `allocate` is asserting not to do :-/

For `OpenStruct` itself that isn't that big a deal, for classes inheriting from `OpenStruct` it breaks `allocate` though.

Example:

~~~ruby
require 'ostruct'

class A < OpenStruct
  def initialize(x, y = {})
    super(y)
  end
end

A.allocate
~~~

As `allocate` is alias'd to `new` in `OpenStruct` this will attempt to initialize `A` which will raise an `ArgumentError` because `A` cannot be initialized without arguments.

~~~
$ ruby x.rb
x.rb:4:in `initialize': wrong number of arguments (given 0, expected 1..2) (ArgumentError)
        from x.rb:9:in `new'
        from x.rb:9:in `<main>'
~~~

OpenStruct at the very least should document the fact that its allocate is behaving differently.
Ideally, `OpenStruct` should not alias allocate at all.




-- 
https://bugs.ruby-lang.org/

Unsubscribe: <mailto:ruby-core-request@ruby-lang.org?subject=unsubscribe>
<http://lists.ruby-lang.org/cgi-bin/mailman/options/ruby-core>