How does rails pass objects to the view?

Question

If an action looks like:

def show
  @post = Post.find(params[:id])
end

I can then do:

<%= @post.title %>

How does it pass the object to the view?

Since my action has only one line, what programming technique or pattern is used to take the @post object and pass it to the view (template) page?

I know it assumes the view will be the same name as the action, but how does it do this?

Answer 1

First you need to look at the binding class. The book "Metaprogramming Ruby" (highly recommended BTW) sums them up nicely: "A Binding is a whole scope packaged as an object. The idea is that you can create a Binding to capture the local scope and carry it around."

Then a look at the ERB class should answer your question. This example is straight from the docs:

  require 'erb'

  x = 42
  template = ERB.new <<-EOF
    The value of x is: <%= x %>
  EOF
  puts template.result(binding)

I hope that helps.

Answer 2

for example like this: we will transfer MyController variables to MyView variables

class MyController
    def my_action
        @my_variable = 100
    end
end

class MyView
    def process_view_with_variables(variables)
        puts variables.inspect # => [{"@my_variable"=>100}]
        variables.each do |var|
            var.each {|name,value| self.instance_variable_set(name,value)}
        end 
        puts self.instance_variables # => @my_variable
        # .. view_rendering here
    end
end

# create new view and controller instances
my_controller = MyController.new
my_view = MyView.new

# call my_action method in MyController instance (which will initialized some variables)
my_controller.my_action

# let know about instance variables in our controller
puts my_controller.instance_variables.inspect # => ["@my_variable"]

# simple array, for store variables (this is like a proxy)
controller_variables = []

# transfer instance variables from controller to proxe
my_controller.instance_variables.each do |variable|
    controller_variables << {variable => my_controller.instance_variable_get(variable)}
end

# let know which instance variables bow in proxy array
puts controller_variables.inspect # => [{"@my_variable"=>100}]

# call method process_view_with_variables which will transfer variables from proxy to view
my_view.process_view_with_variables(controller_variables) # => [{"@my_variable"=>100}]#