Find certain object in Ruby - ruby

Question

Always working with Rails but now that I am coding completely without framework I am missing a lot of methods that I am not able to write myself. So I need a little hint here.
So I've got this code
class Foo
initialize(k)
(1..k).each do |b|
Boo.new(b)
end
end
class Boo
initialize(a)
#a = a
end
end
Foo.new(10)
#and now I want to access one of the Boo's with a certain a (in Rails Boo.find_by_a(2) e.g.)
How do I write a method that uses a certain value "a" to get the specific Boo back with #a = a?
Update:
Okay I added this methot to Boo
def self.all
ObjectSpace.each_object(self).to_a
end
And now I get the right object by:
boo = Boo.all.select{ |b| b.a == 2 }.first
But if I want this to be a method, where would i put it?

Answer 1

DO NOT RELY ON ObjectSpace for this functionality when the GC collects you will lose these objects because Ruby sees them as unneeded.
This is the general concept of what you are intending to do
class Foo
attr_reader :boos
def initialize(k)
#boos = (1..k).map {|b| Boo.new(b) }
end
def find_boo_with(x)
#boos.find {|b| b.a == x }
end
end
class Boo
attr_reader :a
def initialize(a)
#a = a
end
end
Then you can do this
f = Foo.new(10)
f.boos
#=> [#<Boo:0x256f428 #a=1>,
#<Boo:0x256f3b0 #a=2>,
#<Boo:0x256f368 #a=3>,
#<Boo:0x256f338 #a=4>,
#<Boo:0x256f2f0 #a=5>,
#<Boo:0x256f2d8 #a=6>,
#<Boo:0x256f2a8 #a=7>,
#<Boo:0x256f290 #a=8>,
#<Boo:0x256f278 #a=9>,
#<Boo:0x256f260 #a=10>]
f.find_boo_with(9)
#=> #<Boo:0x256f278 #a=9>
I hope this helps but you really should look into something like RubyMonk, or TryRuby to get a better understanding of how PORO (Plain Old Ruby Objects) work.
You could also do it this way if you really wanted your find methodology just know that no Boo in this case will ever be collected as they will all be stored in a class instance variable called #all_boos which could casue memory issues depending on what a Boo is and how many of them you are creating.
class Boo
class << self
def all_boos
#all_boos ||= []
end
def find(x)
#all_boos.find {|boo| boo.a == x }
end
alias_method :all, :all_boos
end
attr_reader :a
def initialize(a)
#a = a
self.class.all_boos << self
end
end
Then you can do
10.times {|i| Boo.new(i) }
Boo.all
#=> [#<Boo:0x256f428 #a=1>,
#<Boo:0x256f3b0 #a=2>,
#<Boo:0x256f368 #a=3>,
#<Boo:0x256f338 #a=4>,
#<Boo:0x256f2f0 #a=5>,
#<Boo:0x256f2d8 #a=6>,
#<Boo:0x256f2a8 #a=7>,
#<Boo:0x256f290 #a=8>,
#<Boo:0x256f278 #a=9>,
#<Boo:0x256f260 #a=10>]
Boo.find(9)
#=> #<Boo:0x256f278 #a=9>

Answer 2

If I did understand what you need then I think that you can use ObjectSpace to achieve this. This is the sample code that illustrates the use:
class Foo
def initialize(k)
(1..k).each do |b|
Boo.new(b)
end
end
end
class Boo
attr_reader :a
def initialize(a)
#a = a
end
def self.find(value)
ObjectSpace.each_object(Boo).select { |b| b.a == value }.first
end
end
Foo.new(10)
Boo.find(2).a
Let me know if this is the solution you were looking for.

Answer 3

Not sure I 100% understand your question but using attr_reader in Boo will allow you to access a as if it were a function.
class Foo
def initialize(k)
(1..k).each do |b|
Boo.new(b)
end
end
end
class Boo
attr_reader :a
def initialize(a)
#a = a
end
end
Foo.new(10)
As for the other part of your question, here is a good article explaining how dynamic finders work