How come this rails magic works?

Question

I'm following this tutorial: http://www.gotealeaf.com/blog/the-detailed-guide-on-how-ajax-works-with-ruby-on-rails

He is using a _task partial to display all the tasks created so far. What I don't understand is why in the partial this line works:

<%= task.deadline %>

Where was the task defined and how does it iterate through all the tasks?

_task.html.erb

<div class="row">
  <div class="col-md-5 col-md-offset-1">
    <h2>Tasks</h2>
  </div>

  <div class="col-md-2 col-md-offset-4">
    <%= link_to new_task_path, remote: true do %>
      <button class="btn btn-default">New</button>
    <% end %>
  </div>
</div>

<div class="row">
  <div class="col-md-6 col-md-offset-2" id="task-form" style="display:none;"></div>
</div>

<div class="row">
  <div class="col-md-7 col-md-offset-1" id="tasks"><%= render @tasks %></div>
</div>

the controller:

class TasksController < ApplicationController
  before_action :all_tasks, only: [:index, :create, :update, :destroy]
  before_action :set_tasks, only: [:edit, :update, :destroy]
  respond_to :html, :js

  def new
    @task = Task.new
  end

  def create
    @task = Task.create(task_params)
  end

  def update
    @task.update_attributes(task_params)
  end

  def destroy
    @task.destroy
  end

  private

    def all_tasks
      @tasks = Task.all
    end

    def set_tasks
      @task = Task.find(params[:id])
    end

    def task_params
      params.require(:task).permit(:description, :deadline)
    end
end

index view:

<div class="row">
  <div class="col-md-5 col-md-offset-1">
    <h2>Tasks</h2>
  </div>

  <div class="col-md-2 col-md-offset-4">
    <%= link_to new_task_path, remote: true do %>
      <button class="btn btn-default">New</button>
    <% end %>
  </div>
</div>

<div class="row">
  <div class="col-md-6 col-md-offset-2" id="task-form" style="display:none;"></div>
</div>

<div class="row">
  <div class="col-md-7 col-md-offset-1" id="tasks"><%= render @tasks %></div>
</div>

Answer 1

<%= render @tasks %> is a shorthand for:

<% @tasks.each do |task| %>
  # task object is available here so you can call task.deadline on it
<% end %>

http://guides.rubyonrails.org/layouts_and_rendering.html#using-partials look for 3.4.5 Rendering Collections