ruby mixin with class methods, instance methods, and class variables

Question

Do you know how to define @@method_names class variable so that both my_macro and invoke_methods can use it as intended? Thank you!

module MyModule

    module ClassMethods    
        def my_macro method_name, options = { }
            define_method method_name do
                puts "defining #{method_name} with #{options}"
            end
            @@method_names << method_name
        end    
    end

    def invoke_methods
        @@method_names.each { |method_name| send method_name }
    end

    def self.included includer
        includer.extend ClassMethods
    end

end

class MyClass
    include MyModule
    my_macro :method_foo, :bar => 5
    my_macro :method_baz, :wee => [3,4]
end

MyClass.new.invoke_methods

Maybe init first @@method_names = [] before @@method_names << method_name — Zabba
– Zabba, Commented Jun 23, 2011 at 19:35
I tried this: @@method_names = [] unless @@method_names; @@method_names << method_name but got NameError: uninitialized class variable @@method_names in MyModule::ClassMethods — Marcos
– Marcos, Commented Jun 23, 2011 at 19:40
Do this instead of using unless: @@method_names = @@method_names || [] — Zabba
– Zabba, Commented Jun 23, 2011 at 19:50

Zabba · Accepted Answer · 2011-06-23 20:25:21Z

2

Here's a working version. Changes are commented:

module MyModule
    module ClassMethods
        @@method_names ||= [] #move this up here
        def my_macro method_name, options = { }
            define_method method_name do
                puts "defining #{method_name} with #{options}"
            end
            @@method_names << method_name
        end

        #added this (rename as required)
        def the_methods
          @@method_names
        end
    end

    def invoke_methods
        #changed this call
        self.class.the_methods.each { |method_name| send method_name }
    end

    def self.included includer
        includer.extend ClassMethods
    end
end

class MyClass
    include MyModule
    my_macro :method_foo, :bar => 5
    my_macro :method_baz, :wee => [3,4]
end

MyClass.new.invoke_methods

answered Jun 23, 2011 at 20:25

Zabba

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Comments

Victor Moroz · Accepted Answer · 2011-06-23 20:15:06Z

1

module MyModule

    module ClassMethods    
        def my_macro method_name, options = { }
            define_method method_name do
                puts "defining #{method_name} with #{options}"
            end
            @method_names ||= []
            @method_names << method_name
        end  

        def method_names
          @method_names
        end  
    end

    def invoke_methods
        self.class.method_names.each { |method_name| send method_name }
    end

    def self.included includer
        includer.extend ClassMethods
    end

end

class MyClass
    include MyModule
    my_macro :method_foo, :bar => 5
    my_macro :method_baz, :wee => [3,4]
end

MyClass.new.invoke_methods

answered Jun 23, 2011 at 20:15

Victor Moroz

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4 Comments

Zabba Over a year ago

How to make it work with class variable instead of instance variable?

Victor Moroz Over a year ago

I don't think it is possible to access a class variable from a class method. @@var in a class method is a very weird thing, don't do it. In general using class variables is not recommended at all, even in "normal" case.

Zabba Over a year ago

It is possible to access a class variable from a class method - not sure what you meant about that(class A; @@m = "hello"; def self.x; p @@m; end; end; A.x; ). But I agree with the rest of your statement.

Victor Moroz Over a year ago

@Zabba Originally "class" variable is @@v defined in the instance method, and such variable is shared between instances of the same class (and also inherited!) : class A; def a; @@a = 1 end; def b; puts @@a end; end; A.new.a; A.new.b. @@v defined in a class context is completely different beast. Why do you need it?

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