= Meta-Magic in Rails: Become a Master Magician by Nic Williams

== Ruby is obviously special

Was writing in .NET
Noticed the RoR marketing machine, promising to write code fast
"I quit being a coder because I hated it - turned out I just hated Java"

== But why?

Data in --> Process --> Data out
Why do I need a specific language?

== Ruby has

=== 1. Flexible syntax

class Post
	attr_accessor(:title)
end

5.times { |n| puts n }

"I'm not the bloke to tell you what to do"

=== 2. Dynamic behaviour

If you don't like a library, just change it

Post.find_by_year_and_month(2007, 9)

user = add_user do
	name "Dr Nic"
	country "Australia"
end

== Perl - Puppy
"Perl is like a puppy - it's fun to use, but it doesn't know anything about itself"
Fowler: "Oh yes it does"
- Cute and fun to use
- No understanding of itself
- Wees on the floor

== Java - Keith Richards
- Not so cute anymore
- Can tell stories about himself
- Can't change his behaviour
- (Should have been dead already)

Java was fun back in the 90's when it first came out. I had to write some Java, and I installed Eclipse, and it was almost fun to use with a decent editor
Keith is very good at talking about himself - but he has no notion about what he is doing, and that he can modidify it

== Ruby - Neo (McGyver, A-Team)
- Knwos about his environment
- Knwos what he can do
- Can adapt behaviours
- Can get the ladies

== Meta programming
The language knows about itself and can describe itself
- is just another library to use

== Introspection (see behaviour)
- What can the code learn about itself?
- Class objects, Interfaces
- Methods, Constructors

=== Java introspection
- Java has it, but it requires a truck-load of code

=== Ruby introspection
- is cleaner

neo = Person.new
neo.class # => Person
neo.methods # => [.. 'activity', 'activity=' ...]
neo.sen("activity=", "Stop bullets in mid-air")

== Reflection (change behaviour)
- See your world
- Change your world

The more important part of meta-programming

=== Java Relection API
- Doesn't actually do anything, should have called the introspection API

=== Ruby

class << Person
	defined_method :show_activity do
		puts self.activity
	end
end

Conceptually, code is data: {:code => "data"}

Ruby is programmable programming language

=== method_missing

Probably the most useful meta-programming tool

Person.find_by_firstname_and_lastname("Nic", "Williams")
rxml views / builder

def method_missing(methid, *args, &block)
	...
	super
end

Please document above what this method makes you able to do, because the code is unreadeable

You could do: 5.to_post instead of Post.find(5)
- Uses this for debugging

=== Create new classes

class Person
end

Person = Class.new

klass = Class.new
Object.const_set "Person", klass # Could be any module

def klass.me
	puts "moi"
end

class << klass
end

klass.class_eval do
	include MyMod
end

==== const_missing

Disappointing that Dave Thomas apologized about talking about Rails
- Dr Nic's Magic Models

A demonstration of what you can do with with meta-progamming
- Allows for dynamic creaton of ActiveRecord classes

== Hpricot(open(url))

How do you use the module as a method?

Hpricot method declared before the class


== eval

eval <<-EOS
	...
EOS

=== class_eval / module_eval

against the Class

=== instance_eval

against an instance


== Gem: guessmethod

Prson.nw.nam


RejeConf tonight at 21.00
http://www.rug-b.de/wiki/show/RejectConf