- Inheritance
The Singleton module implements the Singleton pattern.
Usage:
class Klass
include Singleton
# ...
end
- this ensures that only one instance of Klass lets call it ``the
instance’’ can be created.
a,b = Klass.instance, Klass.instance a == b # => true a.new # NoMethodError - new is private …
- ``The instance’’ is created at instantiation time, in other
words the first call of Klass.instance(), thus
class OtherKlass include Singleton # ... end ObjectSpace.each_object(OtherKlass){} # => 0. - This behavior is preserved under inheritance and cloning.
This is achieved by marking
- Klass.new and Klass.allocate - as private
Providing (or modifying) the class methods
- Klass.inherited(sub_klass) and Klass.clone() - to ensure that the Singleton pattern is properly inherited and cloned.
- Klass.instance() - returning ``the instance’’. After a
successful self modifying (normally the first) call the method body is a
simple:
def Klass.instance() return @__instance__ end - Klass._load(str) - calling Klass.instance()
- Klass._instantiate?() - returning ``the instance’’ or nil. This hook method puts a second (or nth) thread calling Klass.instance() on a waiting loop. The return value signifies the successful completion or premature termination of the first, or more generally, current "instantiation thread".
The instance method of Singleton are
- clone and dup - raising TypeErrors to prevent cloning or duping
- _dump(depth) - returning the empty string. Marshalling strips by default all state information, e.g. instance variables and taint state, from ``the instance’’. Providing custom _load(str) and _dump(depth) hooks allows the (partially) resurrections of a previous state of ``the instance’’.
Methods
Instance
| Visibility | Signature |
|---|---|
| public | clone () |
| public | dup () |
Instance Method Detail
clone()
disable build-in copying methods