Method: TinyDecorator::Delegatable#delegate

Defined in:
lib/tiny_decorator/delegatable.rb

#delegate(*methods, to: nil, prefix: nil, allow_nil: nil) ⇒ Object

File activesupport/lib/active_support/core_ext/module/delegation.rb, line 154 In case we don’t use rails, include their well known delegate I have no idea of how to write it better



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# File 'lib/tiny_decorator/delegatable.rb', line 15

def delegate(*methods, to: nil, prefix: nil, allow_nil: nil)
  unless to
    raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, to: :greeter)."
  end

  if prefix == true && /^[^a-z_]/.match?(to)
    raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method."
  end

  method_prefix = if prefix
      "#{prefix == true ? to : prefix}_"
    else
      ""
    end

  location = caller_locations(1, 1).first
  file, line = location.path, location.lineno

  to = to.to_s
  to = "self.#{to}" if TinyDecorator::Delegatable::DELEGATION_RESERVED_METHOD_NAMES.include?(to)

  methods.map do |method|
    # Attribute writer methods only accept one argument. Makes sure []=
    # methods still accept two arguments.
    definition = /[^\]]=$/.match?(method) ? "arg" : "*args, &block"

    # The following generated method calls the target exactly once, storing
    # the returned value in a dummy variable.
    #
    # Reason is twofold: On one hand doing less calls is in general better.
    # On the other hand it could be that the target has side-effects,
    # whereas conceptually, from the user point of view, the delegator should
    # be doing one call.
    if allow_nil
      method_def = [
        "def #{method_prefix}#{method}(#{definition})",
        "_ = #{to}",
        "if !_.nil? || nil.respond_to?(:#{method})",
        "  _.#{method}(#{definition})",
        "end",
      "end"
      ].join ";"
    else
      exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}")

      method_def = [
        "def #{method_prefix}#{method}(#{definition})",
        " _ = #{to}",
        "  _.#{method}(#{definition})",
        "rescue NoMethodError => e",
        "  if _.nil? && e.name == :#{method}",
        "    #{exception}",
        "  else",
        "    raise",
        "  end",
        "end"
      ].join ";"
    end

    module_eval(method_def, file, line)
  end
end