How can I prevent include one module multi-times?

[Zhao Yi]

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

 

[Peña, Botp]

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[Thomas B.]

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.

 

[James Coglan]

[Note: parts of this message were removed to make it a legal post.]

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.

 

[James Coglan]

[Note: parts of this message were removed to make it a legal post.]

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.

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.