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# ======================
# Spell: Class Extension
# ======================

# Define class methods by mixing a module into a class’s eigenclass
# (a special case of Object Extension - http://gist.github.com/534667).

class C; end

module M

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# ============================
# Spell: Class Extension Mixin
# ============================

# Enable a module to extend its includer through a Hook Method (http://gist.github.com/534994).

module M
  def self.included(base)
    base.extend(ClassMethods)
  end

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# ==============================
# Spell: Class Instance Variable 
# ==============================

# Store class-level state in an instance variable of the Class object.

class C
  @my_class_instance_variable = "some value"

  def self.class_attribute

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# ==================
# Spell: Class Macro
# ==================

# Use a class method in a class definition.

class C; end

class << C
  def my_macro(arg)

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# =================
# Spell: Clean Room
# =================

# Use an object as an environment in which to evaluate a block.

class CleanRoom
  def a_useful_method(x); x * 2; end
end

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# =====================
# Spell: Code Processor
# =====================

# Process Strings of Code (http://gist.github.com/535047) from an external source.

File.readlines("file_containing_lines_of_ruby.txt").each do |line|
  puts "#{line.chomp} ==> #{eval(line)}"
end

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# ====================
# Spell: Context Probe
# ====================

# Execute a block to access information in an object’s context.

class C
  def initialize
    @x = "a private instance variable"
  end

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# ==========================
# Spell: Deferred Evaluation
# ==========================

# Store a piece of code and its context in a proc or lambda for evaluation later.

class C
  def store(&block)
    @my_code_capsule = block
  end

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# =======================
# Spell: Dynamic Dispatch
# =======================

# Decide which method to call at runtime.

method_to_call = :reverse
obj = "abc"

obj.send(method_to_call) # => "cba"

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# =====================
# Spell: Dynamic Method
# =====================

# Decide how to define a method at runtime.

class C
end

C.class_eval do