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Class methods and a conference ( 2019-02-28 )

In short, class methods are working. Plus is some meta stuff that and gotchas that i will explain below. Also i was at presenting rubyx at the first international conference, and there are a couple of misc improvements.

Classes are Singleton objects

Class methods came up when parsing Parfait. To create objects we usually use new, a class method. After briefly contemplating to hack that and use the global space object, i decided to at least check it out. And since it wasn't so bad, i continued.

At some point i thought class methods would be very simple, as they are just methods on another object. After all the way we write code in classes is just a way to define methods on a group of objects. And defining class methods "just" changes which objects we define the methods on. And for the most part, this view is true. The only main difference is that class objects are singletons.

Singletons means singleton classes

Since we want to define methods on the single object, (and we are not programming javascript) we need a class like object that allows us to define these methods and manages them. There are several ways to do this, and i opted for a rather explicit one for now.

So i created a class called MetaClass, that is more or less like a Class. It does currently not derive, just implements the same protocol. In the compiler it can be used as a replacement for a class object, and that is exactly what we do. A metaclass instance is created for every class instance and there is a one to one relation with the class object.

Ruby does this in a more general way, and that off course means that at some point rubyx will have to move there too. In ruby every object has a singleton (meta) class. This must be implemented with lasy creation, otherwise it seems very wasteful. In Ruby the Metaclass is just a class, which means it has a metaclass, and at the moment i have other problems than keeping my brain from melting by thinking in circles like that.

Compiling class methods

Actual compilation now becomes very simple. Before we were passing the class in when compiling a method. Now we have methods and class methods, and depending on which kind it is, we use a different object. The class object for method, and the classes metaclass object for class methods.

Sort of surprisingly, none of the code further down had to be changed. But there are no tests yet for all the possible features, so there may be surprises. Also interpreting a class method call worked straight away, no changes needed there.

Class instance variables also have no tests, and so i don't know if they work or how much work that would be. I sort of hope not much, but there clearly is an issue with the types changing that will have to be addressed.

Change, specifically changing types

As Types never change, we always create new instances. This works for normal objects, as we can just use the new type for new objects. Also while compiling a binary (ie not on the fly yet), we can just use the latest type for all existing objects of a class when we create the binary.

For singletons this hack does not work. Especially when adding class instance variables, the actual type of the existing class object changes. This means we have to change the type reference in the class object. This in turn means the new type has to be binary compatible with the old, which basically means it can't grow beyond the allocated size.

This has been on the horizon for objects since the whole type idea was implemented. Just the horizon was always far away, and now i have to see how much of this can be done easily, how much later. We'll see, tests will tell.

Misc other

Other things have happened that are maybe worth mentioning.

Ruby integer upgrade

Since i started before 2.4 there were still uses of Fixnum. In 2.4 Integer and Fixnum were united and later versions created a whole ton of warning. So i had stuck with 2.3 until now.

Now all Fixnums are gone and i have upgraded to use 2.6.

Object creation

When doing the Factories i hardcoded some page sizes. Hardcoding always bites you, as they should teach everyone in kindergarten, and so it did. It massively increased the test times, as for every Parfait boot (almost every test) several pages worth of objects were created.

I have now made the page size configurable and for good measure am passing some config into the compiler. The compiler then passes a parfait key down, a mechanism that could easily be extended to other subsystems.

The result was that test times have more than halved. Which means my new machine (the one i am just choosing) does not have to be quite as expensive :-)

Command Line Interface

Since i am hoping that people will start playing with ruby-x at some point i thought to make that easier. This has been out there for a while as well, but since the set of features was so small it just didn't get done before.

So now we have a thor based cli in the bin directory. Not that it does so terribly much yet, but at least you can invoke it, get some help, and compile a ruby to binary. Platforms are not supported (as we only have arm) and those Parfait options neither. But a start.

Rubyconf talk

Last but not least, i had the first talk at a conference. At the RubyConf in India, Goa to be specific. Many people were really interested, and Sherif and the organisers we very friendly. Off course we had a nice holiday too. No video yet, but i put the slides up on the homepage.

Work continues

When starting two big projects at work last year i didn't have so much time, and there were months when i had no juice to code. Now i am on part time (physical) work again and am back chipping away at it.

I am still looking for people to join and will increase the effort a bit now that at least a reasonable subset is working.