OO in Parrot Dan Sugalski April 14, 2003

Goals of Parrot OO Support perl 5’s “anything goes” style of objects Support perl 6’s “atrributes and compile- time fixednes” style of objects Support Ruby and Python objects All interchangeably

OO in four parts Outside code using objects Code within parrot-style object classes Class mutation Inheritance

Objects from the outside Objects are opaque They have properties You can call methods on them Other than that, don’t touch

Calling a method Perl 6 $obj.foo();

Calling a method Parrot Assembly clearall find_global P2, “$obj” set S0, “foo” callmeth

Calling a method Parrot Assembly (Fast version) clearall find_global P2, “$obj” set S0, “foo” callmeth.foo_hashed

Parrot class objects Objects are arrays of attributes One slot per attribute of the class and all compatible parent classes Most metadata about objects is stored in the class for the object. This includes slot directories and such

Mutating classes Adding attributes at runtime is possible We’re building a full notification and event system into Parrot Blows caches like mad, so try to avoid this

Inheritance You can inherit from any class Inheriting from ‘foreign’ classes does transparent delegation Delegated objects have parent properties for proper redispatch Opaque classes are a bit of a dead-end

New for Method Invocation Prototypes enforced for methods Method vs Sub invocation known Multimethod dispatch Guaranteed passed-in method names Method tail calls

Introspection No promises in general In practice, lots of opportunities Base object type is completely inspectable

Engine goodies Full notification and event system Method caching (lexically scoped!) Core hash calculations Multimethod dispatch handling Everything can be overridden

Really, everything Property fetching Property storing Returned property hashes Attribute get Attribute set can does isa AUTOLOAD Method lookup Method dispatch Pre and post method calling

Both kinds of objects Both reference and value types Objects have full control over their vtables Full control is yours if you want it Wraps up tying, overloading, and magic Oddly enough, all the object stuff is done as just a custom PMC class--no core changes were needed We’re making some anyway, though

Our plans for world domination Perl 6, Python, and Ruby objects all use the new scheme Transparent inheritance/delegation for perl 5 support