Summer of Code 2006: Ruby Type Inference & Code Completion for RDT

Ruby Type Inference & Code Completion for RDT Google Summer of Code Jason Morrison

Overview
Project Goals
Why Eclipse and Java?
Completion Features
Type Inference Algorithm
Issues
The Future

Project Goals

Project Goals
Code completion for RDT
I’m lazy; Ruby is great and succinct, but…
And, it helps other developers!

Project Goals
Ruby type inference
It’s fun! (Read: I knew very little about it)
Alternative implementation performance
Priming the cache for polymorphic dispatch

Why Eclipse and Java?

“ Eclipse is too big!”

“ It’s bloated! :P”

Not targeting that guy

Convert the natives!

Completion Features

Completion Features
Scoped object completion
Method completion

Scoped Object Completion
Locals, Block Locals
@, @@, $
Pre-defined variables
$_, $:, $”, $0 and friends
Available classes

Scoped Object Completion
Tricky spots:
Open classes
No explicit declaration
set_instance_var and friends

Method Completion
Invocations are message passing
Type is a bag of possible methods
Selector
[Args]
[Confidence]

Method Completion
Many scoping and definition syntaxes:
class Foo;def method;…
instance_eval…
class_eval…
define_method…
include FooModule
Object#extend(module)
class << self; def method;…
method_missing…

What is Type Inference?
Determine the type of an expression
Static analysis
Type versus Class
Not always definitive

Inspired by DDP by Lex Spoon:
Demand-Driven Analysis with Goal Pruning
Type flow analysis
Unions types over contours

DDP Structure
Posts goals
Goals have sub-goals
Answered by judgements
Prunes low value goals
High cost
Low impact on high level goals

DDP Goals
1. Type goal
What is the type of x?
2. Transitive flow
Where can objects flow from x?
3. Simple flow
Where can objects flow from x in one step?
4. Sender
What statements invoke FooClass#bar?
5. Responder
What methods are invoked by "foo.bar"?

DataFlowTypeInferrer
infer(String source, int offset)
findSenders(String scope, String selector)
findMethodDef(String scope, String selector)

DataFlowTypeInferrer

Issues
Eval
Data-bound flow control
return ( rand() > 0.5 ) ? String.new : Array.new
Metaprogramming
Collections
Builtins

The Future
Statistical type inference
Type metadata (collections)
Rails tie-in
AR querying for magic find
Instance vars in View templates
TI for implementation optimizations

Thanks!
Chris Williams, project mentor!
Google Summer of Code
Everyone on the RDT and JRuby teams
All the folks at RubyCentral

Q&A
Jason Morrison
[email_address]
http://soc.jayunit.net

Summer of Code 2006: Ruby Type Inference & Code Completion for RDT

by Jason Morrison on Dec 27, 2007

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