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


Eregon (Benoit Daloze) wrote:
> But not only, after all it is a public and well-known method (many hits on GitHub code search).
> Many deserializing libraries will use it,

Methods of constructed objects will be used more than construction usually.

> but also various libraries which need to build an instance without passing in state,
> or use it as a way to replicate `Class#new` without using super like (maybe to use a different initializing method):

It doesn't need `allocate`, `CACHE[name] || super`.

> The performance hit on `respond_to?` is not significant, it's just an extra `NIL_P`.

And a branch.

> On the other hand, the one on `allocate` is, and affects every caller of `OpenStruct.allocate`.

Why do you think the performance of `allocate` matters?
Note that it is never used in common, since `Class#new` never calls `allocate` overridden in ruby level.


----------------------------------------
Bug #13358: OpenStruct overriding allocate
https://bugs.ruby-lang.org/issues/13358#change-63787

* 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: REQUIRED, 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.




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