Modules and classes question


#1

Hi,

This is a serious noob question.

I am trying to write a small library and have the following situation:

class Main
//initializes connection

def request(blabla)
end
end

class Resource < Main
//different API calls
def call
//bla bla
request(call)
end
end

I would like to let the user do something like the AWS library:
Library::Main.initialize_connection(data) // initializes everything
and then just:
Library::Resource.method // and this should work

In Main I have the function that fills the data, I just don’t know how
to implement the Resource class.


#2

Marcelo B. wrote:

Hi,

This is a serious noob question.

I am trying to write a small library and have the following situation:

class Main
//initializes connection

def request(blabla)
end
end

class Resource < Main
//different API calls
def call
//bla bla
request(call)
end
end

I would like to let the user do something like the AWS library:
Library::Main.initialize_connection(data) // initializes everything
and then just:
Library::Resource.method // and this should work

In Main I have the function that fills the data, I just don’t know how
to implement the Resource class.

I’m not sure what your issue is, so let’s start with this:

module Library

class Main
def Main.initialize_stuff
puts “initializing”
end
end

class Resource
def Resource.meth
puts “executing meth”
end
end

end

Library::Main.initialize_stuff
Library::Resource.meth

–output:–
initializing
executing meth

Now what do you want to do?


#3

Hi,

class Resource
def Resource.meth
puts “executing meth”
end
end

end

Thanks for the answer.

Resource has to call a function from Main, or return an error if Main
isn’t initialized.

I made Resource a subclass of Main because I wanted it to be the main
connection class.


#4

Marcelo B. wrote:

Hi,

class Resource
def Resource.meth
puts “executing meth”
end
end

end

Thanks for the answer.

Resource has to call a function from Main, or return an error if Main
isn’t initialized.

I made Resource a subclass of Main because I wanted it to be the main
connection class.

The next iteration of the code:

module Library

class Main
@@ready_to_go = false

def Main.initialize
  puts "initializing"
  @@ready_to_go = true
end

def Main.do_stuff
  if not @@ready_to_go
    raise "error"
  else
    puts "doing stuff"
  end
end

end

class Resource
def Resource.meth
Main.do_stuff
end
end

end

Library::Main.initialize
Library::Resource.meth

–output:–
initializing
doing stuff


#5

Hi.

The next iteration of the code:

This looks like just what I want. I’ll try it and re-open the thread if
I get stuck again.

Thanks!


#6

7stud – removed_email_address@domain.invalid wrote:

that called meth.
Inside meth, self is equal to the object that meth is inside when it is
called. It has nothing whatever to do with who calls meth. m.


#7

Hi,

class SpecializedResource < BaseResource
def SpecializedResource.meth
sr = SpecializedResource.new
sr.do_stuff
end
end

This seems a little complicated, not very DRY to write this code for
every method.

How does AWS do it?

AWS::S3::Base.establish_connection!()
and then just:
Bucket.create(‘jukebox’)


#8

7stud – wrote:

Another iteration. Try this:

module Library

class BaseResource
@@ready_to_go = false

def BaseResource.initialize
  puts "initializing"
  @@ready_to_go = true
end

def do_stuff
  if not @@ready_to_go
    raise "error"
  else
    puts "doing stuff"
  end
end

end

class SpecializedResource < BaseResource
def SpecializedResource.meth
do_stuff
end
end

end

Library::BaseResource.initialize
Library::SpecializedResource.meth

That doesn’t work. When you write a method call without an object in
front of it:

class SpecializedResource < BaseResource
def SpecializedResource.meth
do_stuff #<-------****
end
end

the implicit caller is self. Inside meth, self is equal to the object
that called meth. The object that called meth can be seen in this line:

Library::SpecializedResource.meth

It’s the class Library::SpecializedResource. So inside meth, self is
equal to the Library::SpecializedResource class. And the
Library:SpecializedResource class does not have a method named
do_stuff–only instances of that class have a method named
do_stuff(which is inherited from BaseResource). To call the instance
method, you need an instance. So you can do something like this:

class SpecializedResource < BaseResource
def SpecializedResource.meth
sr = SpecializedResource.new
sr.do_stuff
end
end


#9

it is thread safe and it is sure that there will and can never be the
need for more than a single connection which seems doubtful in case of
AWS.

I understand. How do you mimic an ActiveResource like structure then?

Something like:
conn = Main.new(user, pass)
conn.resources.method_from_resource_class_that_uses_main_for
the_actual_request_method


#10

2009/5/4 Marcelo B. removed_email_address@domain.invalid:

method.

How does AWS do it?

AWS::S3::Base.establish_connection!()
and then just:
Bucket.create(‘jukebox’)

I do not have insights into AWS beyond what can be gatherere from
http://amazon.rubyforge.org/. I don’t find this pattern very
appealing. For something like this to work you need to resort to some
form of global state (global variable, constant, class instance
variable, thread local variable) which means there is potential for
problems when working with multiple threads. Another issue is that it
is not obvious, i.e. you do not see that there is something
transported behind the scenes.

I would at least refrain from placing this pattern in a library unless
it is thread safe and it is sure that there will and can never be the
need for more than a single connection which seems doubtful in case of
AWS.

My 0.02EUR.

Kind regards

robert


#11

2009/5/5 Marcelo B. removed_email_address@domain.invalid:

I would at least refrain from placing this pattern in a library unless
the_actual_request_method
Yes, or even

Main.connect(user, pass) do |conn|
conn.resources.method_from_resource_class_that_uses_main_for
the_actual_request_method
end

Cheers

robert


#12

the_actual_request_method
end

Right. How do write these classes though?
How would some really really basic Main, Resource classes look like?


#13

2009/5/6 Marcelo B. removed_email_address@domain.invalid:

the_actual_request_method
end

Right. How do write these classes though?
How would some really really basic Main, Resource classes look like?

I’m lacking the time to go into this with more detail but maybe this
blog posting helps you as a start.

http://blog.rubybestpractices.com/posts/rklemme/002_Writing_Block_Methods.html

Note especially the gist with the full code of the example mentioned
at the end of the article.

Kind regards

robert