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# Singleton module that ensures only one object to be allocated.
#
# Usage:
# class SomeSingletonClass
# include Singleton
# #....
# end
# a = SomeSingletonClass.instance
# b = SomeSingletonClass.instance # a and b are same object
# p [a,b]
# a = SomeSingletonClass.new # error (`new' is private)
module Singleton
def Singleton.append_features(klass)
klass.private_class_method(:new)
klass.instance_eval %{
@__instance__ = nil
def instance
Thread.critical = true
unless @__instance__
begin
@__instance__ = new
ensure
Thread.critical = false
end
end
return @__instance__
end
}
end
end
if __FILE__ == $0
class SomeSingletonClass
include Singleton
#....
end
a = SomeSingletonClass.instance
b = SomeSingletonClass.instance # a and b are same object
p [a,b]
a = SomeSingletonClass.new # error (`new' is private)
end
|
