Ruby 2.1 In Detail

112 points by timblair 12 years ago | 12 comments

losvedir 12 years ago |

Funny! I actually came across this article yesterday when trying to look into the current state of Ruby's global method cache. I had a question about the write-up, so maybe I can ask it here!

The page says:

> This is now no longer an issue, Ruby 2.1 uses a method cache based on the class hierarchy, invalidating the cache for only the class in question and any subclasses.

How does this work with an instance of a class? Does it invalidate only that instance's method cache, or all instances in that class? If I do DCI-style:

   @user.extend(PasswordConfirmable)

Does that blow away the cache for all User instances, or just that one?

jxf 12 years ago | |

Just that one. The "class" that the method is attached to here is the metaclass of `@user`.

That class is below `User` in the hierarchy:

    class User; def foo; "foo"; end; end
    # => :foo
    module M; def bar; "bar"; end; end
    # => :bar

    u = User.new
    # => #<User:0x007f2e1abc9e00>
    u.extend M
    # => #<User:0x007f2e1abc9e00>
    
    u.singleton_class.ancestors
    # => [#<Class:#<User:0x007f2e1abc9e00>>,
     M,
     User,
     Object,
     PP::ObjectMixin,
     Kernel,
     BasicObject]

rubiquity 12 years ago | | |

Your example isn't conclusive that what you're saying is true. Your example is just showing that the extended module only appears in the instance's singleton class, this has nothing to do with method cache. It's how the method cache is implemented that matters. The new method caching changes can't be seen from user code.

I'm curious as to whether the ruby-core team implemented method caches for every Object in the system (eg: every instance of User would then have its own method cache because they all would have their own singleton classes) or just objects that are instances of the Class class. I seem to doubt that the former happened because it seems like it would be expensive to maintain a cache for every object, that means a normal Rails request that generates 65,000 strings would all have their own method caches. Only instances of the Class class having their own method caches sounds more reasonable from a performance standpoint to me.

For what it's worth, I've been trying to get an answer about this from a ruby-core member, although my attempts have been quite lazy through Twitter.

ollysb 12 years ago |

There's some great little improvements in there, to_h, required keywords and being able to decorate methods are all things that I regularly want. They're really making good on their philosophy of optimising for developer happiness :)

grey-area 12 years ago |

Hurray, they fixed a little bug I reported: Dir glob returns composed characters. I hit this bug a year or so ago when processing files on OS X.

Thanks to the Ruby team for all the hard work on 2.1, it looks like there's a lot of little changes in there.

anonova 12 years ago |

Does Ruby truly follow semantic versioning now? I still see the patch version.

    $ ruby -v
    ruby 2.1.1p76 (2014-02-24 revision 45161) [x86_64-darwin13.0]

chrisseaton 12 years ago | |

No they don't exactly follow semantic versioning, which is as useful as not following semantic versioning at all.

Specifically, I believe they're planning on breaking API compatibility within major version numbers.

steveklabnik 12 years ago | | |

> Specifically, I believe they're planning on breaking API compatibility within major version numbers.

Yes. Full details: https://www.ruby-lang.org/en/news/2013/12/21/semantic-versio...

timblair 12 years ago | |

The PATCH version is the "number of commits since last MINOR release (will be reset at 0 when releasing MINOR)" — https://www.ruby-lang.org/en/news/2013/12/21/semantic-versio...

class User; def foo; "foo"; end; end # => :foo module M; def bar; "bar"; end; end # => :bar u = User.new # => #<User:0x007f2e1abc9e00> u.extend M # => #<User:0x007f2e1abc9e00> u.singleton_class.ancestors # => [#<Class:#<User:0x007f2e1abc9e00>>, M, User, Object, PP::ObjectMixin, Kernel, BasicObject]