Module: Extlib::Hook::ClassMethods

Extended by:
LocalObjectSpace
Includes:
Assertions
Defined in:
lib/extlib/hook.rb

Instance Method Summary collapse

Methods included from LocalObjectSpace

extended, object_by_id

Methods included from Assertions

#assert_kind_of

Instance Method Details

#after(target_method, method_sym = nil, &block) ⇒ Object

Note:

Either method_sym or block is required.

Inject code that executes after the target instance method.

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# File 'lib/extlib/hook.rb', line 110

def after(target_method, method_sym = nil, &block)
  install_hook :after, target_method, method_sym, :instance, &block
end

#after_class_method(target_method, method_sym = nil, &block) ⇒ Object

Note:

Either method_sym or block is required.

Inject code that executes after the target class method.

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# File 'lib/extlib/hook.rb', line 78

def after_class_method(target_method, method_sym = nil, &block)
  install_hook :after, target_method, method_sym, :class, &block
end

#args_for(method) ⇒ Object

— Helpers —


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# File 'lib/extlib/hook.rb', line 384

def args_for(method)
  if method.arity == 0
    "&block"
  elsif method.arity > 0
    "_" << (1 .. method.arity).to_a.join(", _") << ", &block"
  elsif (method.arity + 1) < 0
    "_" << (1 .. (method.arity).abs - 1).to_a.join(", _") << ", *args, &block"
  else
    "*args, &block"
  end
end

#before(target_method, method_sym = nil, &block) ⇒ Object

Note:

Either method_sym or block is required.

Inject code that executes before the target instance method.

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# File 'lib/extlib/hook.rb', line 94

def before(target_method, method_sym = nil, &block)
  install_hook :before, target_method, method_sym, :instance, &block
end

#before_class_method(target_method, method_sym = nil, &block) ⇒ Object

Note:

Either method_sym or block is required.

Inject code that executes before the target class method.

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# File 'lib/extlib/hook.rb', line 63

def before_class_method(target_method, method_sym = nil, &block)
  install_hook :before, target_method, method_sym, :class, &block
end

#class_hooksObject


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# File 'lib/extlib/hook.rb', line 155

def class_hooks
  self.const_get("CLASS_HOOKS")
end

#define_advised_method(target_method, scope) ⇒ Object


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# File 'lib/extlib/hook.rb', line 283

def define_advised_method(target_method, scope)
  args = args_for(method_with_scope(target_method, scope))

  renamed_target = hook_method_name(target_method, 'hookable_', 'before_advised')

  source = "def \#{target_method}(\#{args})\nretval = nil\ncatch(:halt) do\n\#{hook_method_name(target_method, 'execute_before', 'hook_stack')}(\#{args})\nretval = \#{renamed_target}(\#{args})\n\#{hook_method_name(target_method, 'execute_after', 'hook_stack')}(retval, \#{args})\nretval\nend\nend\n"

  if scope == :instance && !instance_methods(false).any? { |m| m.to_sym == target_method }
    send(:alias_method, renamed_target, target_method)

    proxy_module = Module.new
    proxy_module.class_eval(source, __FILE__, __LINE__)
    self.send(:include, proxy_module)
  else
    source = %{alias_method :#{renamed_target}, :#{target_method}\n#{source}}
    source = %{class << self\n#{source}\nend} if scope == :class
    class_eval(source, __FILE__, __LINE__)
  end
end

#define_hook_stack_execution_methods(target_method, scope) ⇒ Object

Defines two methods. One method executes the before hook stack. The other executes the after hook stack. This method will be called many times during the Class definition process. It should be called for each hook that is defined. It will also be called when a hook is redefined (to make sure that the arity hasn't changed).


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# File 'lib/extlib/hook.rb', line 233

def define_hook_stack_execution_methods(target_method, scope)
  unless registered_as_hook?(target_method, scope)
    raise ArgumentError, "#{target_method} has not be registered as a hookable #{scope} method"
  end

  hooks = hooks_with_scope(scope)

  before_hooks = hooks[target_method][:before]
  before_hooks = before_hooks.map{ |info| inline_call(info, scope) }.join("\n")

  after_hooks  = hooks[target_method][:after]
  after_hooks  = after_hooks.map{ |info| inline_call(info, scope) }.join("\n")

  before_hook_name = hook_method_name(target_method, 'execute_before', 'hook_stack')
  after_hook_name  = hook_method_name(target_method, 'execute_after',  'hook_stack')

  hooks[target_method][:in].class_eval "\#{scope == :class ? 'class << self' : ''}\n\nprivate\n\nremove_method :\#{before_hook_name} if instance_methods(false).any? { |m| m.to_sym == :\#{before_hook_name} }\ndef \#{before_hook_name}(*args)\n\#{before_hooks}\nend\n\nremove_method :\#{after_hook_name} if instance_methods(false).any? { |m| m.to_sym == :\#{after_hook_name} }\ndef \#{after_hook_name}(*args)\n\#{after_hooks}\nend\n\n\#{scope == :class ? 'end' : ''}\n", __FILE__, __LINE__ + 1
end

#hook_method_name(target_method, prefix, suffix) ⇒ Object

Generates names for the various utility methods. We need to do this because the various utility methods should not end in = so, while we're at it, we might as well get rid of all punctuation.


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# File 'lib/extlib/hook.rb', line 203

def hook_method_name(target_method, prefix, suffix)
  target_method = target_method.to_s

  case target_method[-1,1]
    when '?' then "#{prefix}_#{target_method[0..-2]}_ques_#{suffix}"
    when '!' then "#{prefix}_#{target_method[0..-2]}_bang_#{suffix}"
    when '=' then "#{prefix}_#{target_method[0..-2]}_eq_#{suffix}"
    # I add a _nan_ suffix here so that we don't ever encounter
    # any naming conflicts.
    else "#{prefix}_#{target_method[0..-1]}_nan_#{suffix}"
  end
end

#hooks_with_scope(scope) ⇒ Object

Returns the correct HOOKS Hash depending on whether we are working with class methods or instance methods


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# File 'lib/extlib/hook.rb', line 147

def hooks_with_scope(scope)
  case scope
    when :class    then class_hooks
    when :instance then instance_hooks
    else raise ArgumentError, 'You need to pass :class or :instance as scope'
  end
end

#inline_call(method_info, scope) ⇒ Object

Returns ruby code that will invoke the hook. It checks the arity of the hook method and passes arguments accordingly.


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# File 'lib/extlib/hook.rb', line 270

def inline_call(method_info, scope)
  Extlib::Hook::ClassMethods.hook_scopes << method_info[:from]
  name = method_info[:name]

  if scope == :instance
    args = method_defined?(name) && instance_method(name).arity != 0 ? '*args' : ''
    %(#{name}(#{args}) if self.class <= Extlib::Hook::ClassMethods.object_by_id(#{method_info[:from].object_id}))
  else
    args = respond_to?(name) && method(name).arity != 0 ? '*args' : ''
    %(#{name}(#{args}) if self <= Extlib::Hook::ClassMethods.object_by_id(#{method_info[:from].object_id}))
  end
end

#install_hook(type, target_method, method_sym, scope, &block) ⇒ Object

— Add a hook —


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# File 'lib/extlib/hook.rb', line 315

def install_hook(type, target_method, method_sym, scope, &block)
  assert_kind_of 'target_method', target_method, Symbol
  assert_kind_of 'method_sym',    method_sym,    Symbol unless method_sym.nil?
  assert_kind_of 'scope',         scope,         Symbol

  if !block_given? and method_sym.nil?
    raise ArgumentError, "You need to pass 2 arguments to \"#{type}\"."
  end

  if method_sym.to_s[-1,1] == '='
    raise ArgumentError, "Methods ending in = cannot be hooks"
  end

  unless [ :class, :instance ].include?(scope)
    raise ArgumentError, 'You need to pass :class or :instance as scope'
  end

  if registered_as_hook?(target_method, scope)
    hooks = hooks_with_scope(scope)

    #if this hook is previously declared in a sibling or cousin we must move the :in class
    #to the common ancestor to get both hooks to run.
    if !(hooks[target_method][:in] <=> self)
      before_hook_name = hook_method_name(target_method, 'execute_before', 'hook_stack')
      after_hook_name  = hook_method_name(target_method, 'execute_after',  'hook_stack')

      hooks[target_method][:in].class_eval "remove_method :\#{before_hook_name} if instance_methods(false).any? { |m| m.to_sym == :\#{before_hook_name} }\ndef \#{before_hook_name}(*args)\nsuper\nend\n\nremove_method :\#{after_hook_name} if instance_methods(false).any? { |m| m.to_sym == :\#{before_hook_name} }\ndef \#{after_hook_name}(*args)\nsuper\nend\n", __FILE__, __LINE__ + 1

      while !(hooks[target_method][:in] <=> self) do
        hooks[target_method][:in] = hooks[target_method][:in].superclass
      end

      define_hook_stack_execution_methods(target_method, scope)
      hooks[target_method][:in].class_eval{define_advised_method(target_method, scope)}
    end
  else
    register_hook(target_method, scope)
    hooks = hooks_with_scope(scope)
  end

  #if  we were passed a block, create a method out of it.
  if block
    method_sym = "__hooks_#{type}_#{quote_method(target_method)}_#{hooks[target_method][type].length}".to_sym
    if scope == :class
      meta_class.instance_eval do
        define_method(method_sym, &block)
      end
    else
      define_method(method_sym, &block)
    end
  end

  # Adds method to the stack an redefines the hook invocation method
  hooks[target_method][type] << { :name => method_sym, :from => self }
  define_hook_stack_execution_methods(target_method, scope)
end

#instance_hooksObject


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# File 'lib/extlib/hook.rb', line 159

def instance_hooks
  self.const_get("INSTANCE_HOOKS")
end

#method_with_scope(name, scope) ⇒ Object


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# File 'lib/extlib/hook.rb', line 396

def method_with_scope(name, scope)
  case scope
    when :class    then method(name)
    when :instance then instance_method(name)
    else raise ArgumentError, 'You need to pass :class or :instance as scope'
  end
end

#process_method_added(method_name, scope) ⇒ Object

This will need to be refactored


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# File 'lib/extlib/hook.rb', line 217

def process_method_added(method_name, scope)
  hooks_with_scope(scope).each do |target_method, hooks|
    if hooks[:before].any? { |hook| hook[:name] == method_name }
      define_hook_stack_execution_methods(target_method, scope)
    end

    if hooks[:after].any? { |hook| hook[:name] == method_name }
      define_hook_stack_execution_methods(target_method, scope)
    end
  end
end

#quote_method(name) ⇒ Object


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# File 'lib/extlib/hook.rb', line 404

def quote_method(name)
  name.to_s.gsub(/\?$/, '_q_').gsub(/!$/, '_b_').gsub(/=$/, '_eq_')
end

#register_class_hooks(*hooks) ⇒ Object

Register a class method as hookable. Registering a method means that before hooks will be run immediately before the method is invoked and after hooks will be called immediately after the method is invoked.

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# File 'lib/extlib/hook.rb', line 122

def register_class_hooks(*hooks)
  hooks.each { |hook| register_hook(hook, :class) }
end

#register_hook(target_method, scope) ⇒ Object

Registers a method as hookable. Registering hooks involves the following process

  • Create a blank entry in the HOOK Hash for the method.

  • Define the methods that execute the before and after hook stack. These methods will be no-ops at first, but everytime a new hook is defined, the methods will be redefined to incorporate the new hook.

  • Redefine the method that is to be hookable so that the hook stacks are invoked approprietly.


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# File 'lib/extlib/hook.rb', line 172

def register_hook(target_method, scope)
  if scope == :instance && !method_defined?(target_method)
    raise ArgumentError, "#{target_method} instance method does not exist"
  elsif scope == :class && !respond_to?(target_method)
    raise ArgumentError, "#{target_method} class method does not exist"
  end

  hooks = hooks_with_scope(scope)

  if hooks[target_method].nil?
    hooks[target_method] = {
      # We need to keep track of which class in the Inheritance chain the
      # method was declared hookable in. Every time a child declares a new
      # hook for the method, the hook stack invocations need to be redefined
      # in the original Class. See #define_hook_stack_execution_methods
      :before => [], :after => [], :in => self
    }

    define_hook_stack_execution_methods(target_method, scope)
    define_advised_method(target_method, scope)
  end
end

#register_instance_hooks(*hooks) ⇒ Object

Register aninstance method as hookable. Registering a method means that before hooks will be run immediately before the method is invoked and after hooks will be called immediately after the method is invoked.

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# File 'lib/extlib/hook.rb', line 134

def register_instance_hooks(*hooks)
  hooks.each { |hook| register_hook(hook, :instance) }
end

#registered_as_hook?(target_method, scope) ⇒ Boolean

Is the method registered as a hookable in the given scope.


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# File 'lib/extlib/hook.rb', line 196

def registered_as_hook?(target_method, scope)
  ! hooks_with_scope(scope)[target_method].nil?
end

#reset_hook!(target_method, scope) ⇒ Object

Not yet implemented

Raises:

  • (NotImplementedError)

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# File 'lib/extlib/hook.rb', line 139

def reset_hook!(target_method, scope)
  raise NotImplementedError
end