How can I prevent include one module multi-times?

ruby-talk
1

I am looking for a method to check whether this module has been
included. Does Ruby have this feature?

···

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2

# I am looking for a method to check whether this module has been
# included. Does Ruby have this feature?

you can query the class/module thru #included_modules

eg,

class C
end

=> nil

C.included_modules

=> [Kernel]

module M
end

=> nil

class C
include M
end

=> C

C.included_modules

=> [M, Kernel]

or if you want to query the whole program space, search the ObjectSpace

eg,

ObjectSpace.each_object(Module).select{|m| m.class.name == "Module"}

=> [IRB, Exception2MessageMapper, Marshal, ObjectSpace, GC, Math, Process::Sys, Process::GID, Process::UID, Process, Signal, File::Constants, FileTest, Errno, Precision, Enumerable, Comparable, Kernel, Readline, RubyToken, IRB::Notifier, M, IRB::MethodExtender, IRB::ContextExtender, IRB::ExtendCommandBundle]

kind regards -botp

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From: Zhao Yi [mailto:youhaodeyi@gmail.com]

3

Zhao Yi wrote:

I am looking for a method to check whether this module has been
included. Does Ruby have this feature?

Might try parsing Object.constants for the module name.

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4

Zhao Yi wrote:

I am looking for a method to check whether this module has been
included. Does Ruby have this feature?

What's your question? In the subject you ask 'How can I prevent include
one module multi-times?' and this is checked automatically without any
special handling.

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5

That's partially correct, but you'll find that the module's included() hook
gets called repeatedly:

module M
  def self.included(base)
    puts "included M"
  end
end

class C
  # prints "included M" 3 times
  include M
  include M
  include M
end

To check whether M is already mixed into C, the expression 'M > C' returns
true if C includes M. You could put this check inside M.included and throw
an exception if it's true.

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2008/9/3 Thomas B. <tpreal@gmail.com>

Zhao Yi wrote:
> I am looking for a method to check whether this module has been
> included. Does Ruby have this feature?

What's your question? In the subject you ask 'How can I prevent include
one module multi-times?' and this is checked automatically without any
special handling.

6

Roger Pack wrote:

Zhao Yi wrote:
> I am looking for a method to check whether this module has been
> included. Does Ruby have this feature?

Might try parsing Object.constants for the module name.

Why? That only tells you whether that module exists (and it only tells you
that when the module is in the top-level namespace). It doesn't tell you
whether that module has been included into anything.

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7

I should have mentioned that including a module multiple times will not have
any nasty side effects on the inheritance tree of the including class --
this is checked for you.

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2008/9/3 James Coglan <jcoglan@googlemail.com>

2008/9/3 Thomas B. <tpreal@gmail.com>

Zhao Yi wrote:
> I am looking for a method to check whether this module has been
> included. Does Ruby have this feature?

What's your question? In the subject you ask 'How can I prevent include
one module multi-times?' and this is checked automatically without any
special handling.

That's partially correct, but you'll find that the module's included() hook
gets called repeatedly:

module M
  def self.included(base)
    puts "included M"
  end
end

class C
  # prints "included M" 3 times
  include M
  include M
  include M
end

To check whether M is already mixed into C, the expression 'M > C' returns
true if C includes M. You could put this check inside M.included and throw
an exception if it's true.

8

Ah, I think I misunderstood the question. I wrote this a while ago to find
all the descendants of a module:

class Module
  def descendants
    classes =
    ObjectSpace.each_object do |klass|
      next unless Module === klass
      classes << klass if self > klass
    end
    classes
  end
end

So, a module has been included if

mod.descendants.size.nonzero?

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2008/9/3 Sebastian Hungerecker <sepp2k@googlemail.com>

Roger Pack wrote:
> Zhao Yi wrote:
> > I am looking for a method to check whether this module has been
> > included. Does Ruby have this feature?
>
> Might try parsing Object.constants for the module name.

Why? That only tells you whether that module exists (and it only tells you
that when the module is in the top-level namespace). It doesn't tell you
whether that module has been included into anything.

9

Ah, I think I misunderstood the question. I wrote this a while ago to
find
all the descendants of a module:

ah--if the problem is determining if a descendant exists, you could
write an included(instance) method within the included Module to track.
Cheers.
-=R

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