module AbstractController::Helpers::ClassMethods

# File actionpack/lib/abstract_controller/helpers.rb, line 117
def clear_helpers
  inherited_helper_methods = _helper_methods
  self._helpers = Module.new
  self._helper_methods = Array.new

  inherited_helper_methods.each { |meth| helper_method meth }
  default_helper_module! unless anonymous?
end

Clears up all existing helpers in this class, only keeping the helper with the same name as this class.

# File actionpack/lib/abstract_controller/helpers.rb, line 107
def helper(*args, &block)
  modules_for_helpers(args).each do |mod|
    add_template_helper(mod)
  end

  _helpers.module_eval(&block) if block_given?
end

The helper class method can take a series of helper module names, a block, or both.

Options

• *args - Module, Symbol, String

• block - A block defining helper methods

When the argument is a module it will be included directly in the template class.

helper FooHelper # => includes FooHelper

When the argument is a string or symbol, the method will provide the “_helper” suffix, require the file and include the module in the template class. The second form illustrates how to include custom helpers when working with namespaced controllers, or other cases where the file containing the helper definition is not in one of Rails' standard load paths:

helper :foo             # => requires 'foo_helper' and includes FooHelper
helper 'resources/foo'  # => requires 'resources/foo_helper' and includes Resources::FooHelper

Additionally, the helper class method can receive and evaluate a block, making the methods defined available to the template.

# One line
helper { def hello() "Hello, world!" end }

# Multi-line
helper do
  def foo(bar)
    "#{bar} is the very best"
  end
end

Finally, all the above styles can be mixed together, and the helper method can be invoked with a mix of symbols, strings, modules and blocks.

helper(:three, BlindHelper) { def mice() 'mice' end }

# File actionpack/lib/abstract_controller/helpers.rb, line 60
      def helper_method(*meths)
        meths.flatten!
        self._helper_methods += meths

        meths.each do |meth|
          _helpers.class_eval <<-ruby_eval, __FILE__, __LINE__ + 1
            def #{meth}(*args, &blk)                               # def current_user(*args, &blk)
              controller.send(%(#{meth}), *args, &blk)             #   controller.send(:current_user, *args, &blk)
            end                                                    # end
          ruby_eval
        end
      end

Declare a controller method as a helper. For example, the following makes the current_user and logged_in? controller methods available to the view:

class ApplicationController < ActionController::Base
  helper_method :current_user, :logged_in?

  def current_user
    @current_user ||= User.find_by(id: session[:user])
  end

  def logged_in?
    current_user != nil
  end
end

In a view:

<% if logged_in? -%>Welcome, <%= current_user.name %><% end -%>

Parameters

• method[, method] - A name or names of a method on the controller to be made available on the view.

# File actionpack/lib/abstract_controller/helpers.rb, line 32
def inherited(klass)
  helpers = _helpers
  klass._helpers = Module.new { include helpers }
  klass.class_eval { default_helper_module! } unless klass.anonymous?
  super
end

When a class is inherited, wrap its helper module in a new module. This ensures that the parent class's module can be changed independently of the child class's.

# File actionpack/lib/abstract_controller/helpers.rb, line 143
def modules_for_helpers(args)
  args.flatten.map! do |arg|
    case arg
    when String, Symbol
      file_name = "#{arg.to_s.underscore}_helper"
      begin
        require_dependency(file_name)
      rescue LoadError => e
        raise AbstractController::Helpers::MissingHelperError.new(e, file_name)
      end

      mod_name = file_name.camelize
      begin
        mod_name.constantize
      rescue LoadError
        # dependencies.rb gives a similar error message but its wording is
        # not as clear because it mentions autoloading. To the user all it
        # matters is that a helper module couldn't be loaded, autoloading
        # is an internal mechanism that should not leak.
        raise NameError, "Couldn't find #{mod_name}, expected it to be defined in helpers/#{file_name}.rb"
      end
    when Module
      arg
    else
      raise ArgumentError, "helper must be a String, Symbol, or Module"
    end
  end
end

Returns a list of modules, normalized from the acceptable kinds of helpers with the following behavior:

String or Symbol

:FooBar or “FooBar” becomes “foo_bar_helper”,

and “foo_bar_helper.rb” is loaded using require_dependency.

Module

No further processing

After loading the appropriate files, the corresponding modules are returned.

Parameters

• args - An array of helpers

Returns

• Array - A normalized list of modules for the list of helpers provided.