[ANN] traits-0.9.0


A

ara.t.howard

URLS

http://rubyforge.org/projects/codeforpeople/
http://codeforpeople.com/lib/ruby/traits

ABOUT

traits.rb is set of attr_* like methods on steroids, caffeine, and botox. it
encourages better living through meta-programming and uniform access
priciples. traits.rb supports smart inheritence of class attributes and a
fistful of hooks for veryifying and munging attr values.

VERSION

0.9.0

AUTHOR

ara [dot] t [dot] howard [at] noaa [dot] gov

SAMPLES

<========< sample/a.rb >========>

~ > cat sample/a.rb

require 'traits'
#
# defining a trait is like attr_accessor in the simple case
#
class C
trait :t
end

o = C::new
o.t = 42
p o.t

#
# and can be made even shorter
#

class B; has :x; end

o = B::new
o.x = 42
p o.x


~ > ruby sample/a.rb

42
42


<========< sample/b.rb >========>

~ > cat sample/b.rb

require 'traits'
#
# multiple traits can be defined at once using a list/array of string/sybmol
# arguments
#
class C
has :t0, :t1
has %w( t2 t3 )
end

obj = C::new
obj.t0 = 4
obj.t3 = 2
print obj.t0, obj.t3, "\n"

~ > ruby sample/b.rb

42


<========< sample/c.rb >========>

~ > cat sample/c.rb

require 'traits'
#
# a hash argument can be used to specify default values
#
class C
has 'a' => 4, :b => 2
end

o = C::new
print o.a, o.b, "\n"

#
# and these traits are smartly inherited
#
class K < C; end

o = K::new
o.a = 40
p( o.a + o.b ) # note that we pick up a default b from C class here since it
# has not been set

o.a = 42
o.b = nil
p( o.b || o.a ) # but not here since we've explicitly set it to nil

#
# if a block is specifed as the default the initialization of the default value
# is deferred until needed which makes for quite natural trait definitions. the
# block is passed 'self' so references to the current object can be made. (if
# this were not done 'self' in the block would be bound to the class!)
#

class C
class << self
has('classname'){ name.upcase }
end

has('classname'){ self.class.classname.downcase }
end

class B < C; end

o = C::new
p C::classname
p o.classname

o = B::new
p B::classname
p o.classname

~ > ruby sample/c.rb

42
42
42
"C"
"c"
"B"
"b"


<========< sample/d.rb >========>

~ > cat sample/d.rb

require 'traits'
#
# all behaviours work within class scope (metal/singleton-class) to define
# class methods
#
class C
class << self
traits 'a' => 4, 'b' => 2
end
end

print C::a, C::b, "\n"

#
# singleton methods can even be defined on objects
#

class << (a = %w[dog cat ostrich])
has 'category' => 'pets'
end
p a.category

#
# and modules
#
module Mmmm
class << self; trait 'good' => 'bacon'; end
end

p Mmmm.good

~ > ruby sample/d.rb

42
"pets"
"bacon"


<========< sample/e.rb >========>

~ > cat sample/e.rb

require 'traits'
#
# shorhands exit to enter 'class << self' in order to define class traits
#
class C
class_trait 'a' => 4
c_has :b => 2
end

print C::a, C::b, "\n"

~ > ruby sample/e.rb

42


<========< sample/f.rb >========>

~ > cat sample/f.rb

require 'traits'
#
# as traits are defined they are remembered and can be accessed
#
class C
class_trait :first_class_method
trait :first_instance_method
end

class C
class_trait :second_class_method
trait :second_instance_method
end

#
# readers and writers are remembered separatedly
#
p C::class_reader_traits
p C::instance_writer_traits

#
# and can be gotten together at class or instance level
#
p C::class_traits
p C::traits

~ > ruby sample/f.rb

["first_class_method", "second_class_method"]
["first_instance_method=", "second_instance_method="]
[["first_class_method", "first_class_method="], ["second_class_method", "second_class_method="]]
[["first_instance_method", "first_instance_method="], ["second_instance_method", "second_instance_method="]]


<========< sample/g.rb >========>

~ > cat sample/g.rb

require 'traits'
#
# another neat feature is that they are remembered per hierarchy
#
class C
class_traits :base_class_method
trait :base_instance_method
end

class K < C
class_traits :derived_class_method
trait :derived_instance_method
end

p C::class_traits
p K::class_traits

~ > ruby sample/g.rb

[["base_class_method", "base_class_method="]]
[["derived_class_method", "derived_class_method="], ["base_class_method", "base_class_method="]]


<========< sample/h.rb >========>

~ > cat sample/h.rb

require 'traits'
#
# a depth first search path is used to find defaults
#
class C
has 'a' => 42
end
class K < C; end

k = K::new
p k.a

#
# once assigned this is short-circuited
#
k.a = 'forty-two'
p k.a

~ > ruby sample/h.rb

42
"forty-two"


<========< sample/i.rb >========>

~ > cat sample/i.rb

require 'traits'
#
# getters and setters can be defined separately
#
class C
has_r :r
end
class D
has_w :w
end

#
# defining a reader trait still defines __public__ query and __private__ writer
# methods
#
class C
def using_private_writer_and_query
p r?
self.r = 42
p r
end
end
C::new.using_private_writer_and_query

#
# defining a writer trait still defines __private__ query and __private__ reader
# methods
#
class D
def using_private_reader
p w?
self.w = 'forty-two'
p w
end
end
D::new.using_private_reader

~ > ruby sample/i.rb

false
42
false
"forty-two"


<========< sample/j.rb >========>

~ > cat sample/j.rb

require 'traits'
#
# getters delegate to setters iff called with arguments
#
class AbstractWidget
class_trait 'color' => 'pinky-green'
class_trait 'size' => 42
class_trait 'shape' => 'square'

# we define instance traits which get their default from the class
%w( color size shape ).each{|t| trait(t){self.class.send t}}

def inspect
"color <#{ color }> size <#{ size }> shape <#{ shape }>"
end
end

class BlueWidget < AbstractWidget
color 'blue'
size 420
end

p BlueWidget::new

~ > ruby sample/j.rb

color <blue> size <420> shape <square>


<========< sample/k.rb >========>

~ > cat sample/k.rb

require 'traits'
#
# the rememberance of traits can make generic intializers pretty slick
#
class C
#
# define class traits with defaults
#
class_traits(
'a' => 40,
'b' => 1,
'c' => 0
)

#
# define instance traits whose defaults come from readable class ones
#
class_rtraits.each{|ct| instance_trait ct => send(ct)}

#
# any option we respond_to? clobbers defaults
#
def initialize opts = {}
opts.each{|k,v| send(k,v) if respond_to? k}
end

#
# show anything we can read
#
def inspect
self.class.rtraits.inject(0){|n,t| n += send(t)}
end
end

c = C::new 'c' => 1
p c

~ > ruby sample/k.rb

42


<========< sample/l.rb >========>

~ > cat sample/l.rb

require 'traits'
#
# even defining single methods on object behaves
#
a = []

class << a
trait 'singleton_class' => class << self;self;end

class << self
class_trait 'x' => 42
end
end

p a.singleton_class.x

~ > ruby sample/l.rb

42


<========< sample/m.rb >========>

~ > cat sample/m.rb

require 'traits'
#
# pre and post hooks can be passed a proc or the name of a method, the arity is
# detected and the proc/method sent either the value, or the name/value pair
#

class C
HOOK_A = lambda{|value| puts "HOOK_A : #{ value }"}
HOOK_B = lambda{|name, value| puts "HOOK_B : #{ name } = #{ value }"}

def hook_a value
puts "hook_a : #{ value }"
end
def hook_b name, value
puts "hook_b : #{ name } = #{ value }"
end

trait 'x', 'pre' => HOOK_A, 'post' => 'hook_b'
trait 'y', 'pre' => HOOK_B, 'post' => 'hook_a'
end

c = C::new
c.x = 42
c.y = 'forty-two'

~ > ruby sample/m.rb

HOOK_A : 42
hook_b : x = 42
HOOK_B : y = forty-two
hook_a : forty-two


<========< sample/n.rb >========>

~ > cat sample/n.rb

require 'traits'
#
# two kinds of in-place modifications are supported : casting and munging.
# casting is a hook that requires either a proc or the name of a method that
# will be used to convert the objects type. munging is similar execpt the
# method is called on the object itself. like all hooks, lists may be provided
# instead of a single argument
#
# you'll notice that the hooks and methods defined here are not strictly needed,
# but are for illustration purposes only. note that all hooks operate in the
# context of self - they have access to instance vars, etc., like instance_eval
#

class C
INT = lambda{|i| int i}
def int i
Integer i
end
trait 'a', 'cast' => 'int'
trait 'b', 'cast' => INT
trait 'c', 'munge' => 'to_i'
trait 'd', 'cast' => 'Integer'
trait 'e', 'munge' => %w( to_i abs )
end

c = C::new

c.a = '42'
p c.a
c.b = '42'
p c.b
c.c = '42'
p c.c
c.d = '42'
p c.d
c.e = '-42'
p c.e

~ > ruby sample/n.rb

42
42
42
42
42


<========< sample/p.rb >========>

~ > cat sample/p.rb

require 'traits'
#
# the TraitInit module provide a simple method for initializing an object's
# traits from an options hash
#

class C
include TraitInit

LIST_OF_INTS = lambda{|a| Array === a and a.map{|i| Integer === i}.all?}
LIST_OF_STRINGS = lambda{|a| Array === a and a.map{|s| String === s}.all?}

trait :li, :validate => LIST_OF_INTS
trait :ls, :validate => LIST_OF_STRINGS

def initialize opts = {}
trait_init opts
end
end

c = C::new "li" => [4, 2], "ls" => %w[4 2]
p c.li.join
p c.ls.join

~ > ruby sample/p.rb

"42"
"42"


CAVEATS

this library is experimental and subject to change - though it has not for
several versions and much of my code hinges is on it now so you can expect the
interface to be stable in the near future - the only changes planned are those
that fix bugs or add features.


LICENSE

same as ruby's


HISTORY

0.9.0
- luke kaines made quite a few suggestions and bug reports that enabled this
release including making a few methods indifferent about string/symbol
args/keys and the introduction of a simple method 'trait_init' that can be
used to create keyword based initializers, eg:

require 'traits'

class C
include TraitInit

trait :a, :type => Integer
trait :b, :type => Integer

def initialize opts = {}
trait_init opts
end
end

C::new :a => 4, :b => 2

0.8.0
- traits now supports a whole slew of hooks that can be registered to fire
pre or post setting an attribute, to cast a value to another type, to
munge a value destructively, to require only certain types, to require a
certain ducktype signature, and to validate arguments passed. check out
sample/m.rb, sample/n.rb, or sample.o.rb to see it in action. the
mechanism is quite flexible allowing method names, lambdas of varying
arity, and lists of either/or to be passed to any hook.

- you can find a gem for trais on codeforpeople - but i've still not coded
up automated updating from codeforpeople to rubyforge so it won't show up
as a remote gem yet.

0.7.0
- patched in the support i had written eariler for 'hooks' to be called
pre/post setting a trait. plus shortcut to 'validate' traits which simply
sets up a 'pre' hook which is used as a predicate. eg:

class C; trait 'number', 'validate' => proc{|n| Numeric === n}

pre and post hooks are used in the same way, eg:

class C
trait 'a',
'pre' => proc{|val| p "#{ val } to set with"},
'post' => proc{|val| p "#{ val } set"},
end

but the really cool thing is that all of these blocks are both passed the
value in question but also evaluate with 'self' set appropriately. eg

class Car
positive_int = lambda{|n| Fixnum === n and n > 0}
legal = proc{|s| s < speed_limit}

trait 'speed_limit', 'validate' => positive_int, 'default' => 42
trait 'speed', 'validate' => legal
end

c = Car::new
c.speed = 115

works as you'd expect:

(eval):14:in `speed=': validation of speed=(115) failed! (ArgumentError)
from a.rb:13

0.6.0
- fixed bug in where a default trait given as an empty array, eg:

class C; has 'a' => []; end

was exploded into the empty list when passed to the setter to initialize
the default value.

0.5.0
- general code cleanup

0.4.0
- tweaked writer code so multiple values can be passed to setters
- tweaked method of running blocks to use instance_eval so explicit 'this'
arg is no longer needed (though it can still be used)

0.3.0
added ability of default values to be specified with block for deferred
context sensitive initialization (see sample/c.rb)

0.1.0

completely reworked impl so NO parsing of inspect strings is required -
it's all straight methods (albeit quite confusing ones) now. the
interface is unchanged.

0.0.0

initial version




enjoy.


-a
--
===============================================================================
| ara [dot] t [dot] howard [at] noaa [dot] gov
| all happiness comes from the desire for others to be happy. all misery
| comes from the desire for oneself to be happy.
| -- bodhicaryavatara
===============================================================================
 
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A

ara.t.howard

Ara,

What's new in this version of traits?

the absence of a few hard to hit but real bugs - most importantly that

trait 'foo', 'type' => Pathname
trait 'foo', :type => Pathname

behaved differently and a few related bugs.

not to much otherwise. if you are happy you don't need to upgrade.

cheers.

-a
--
===============================================================================
| ara [dot] t [dot] howard [at] noaa [dot] gov
| all happiness comes from the desire for others to be happy. all misery
| comes from the desire for oneself to be happy.
| -- bodhicaryavatara
===============================================================================
 

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