--- !ruby/object:RI::ClassDescription
attributes: []
class_methods: []
comment:
- !ruby/struct:SM::Flow::P
body: The Singleton module implements the Singleton pattern.
- !ruby/struct:SM::Flow::P
body: "Usage:"
- !ruby/struct:SM::Flow::VERB
body: " class Klass\n include Singleton\n # ...\n end\n"
- !ruby/object:SM::Flow::LIST
contents:
- !ruby/struct:SM::Flow::LI
label: "*"
body: this ensures that only one instance of Klass lets call it ``the instance'' can be created.
- !ruby/struct:SM::Flow::P
body: "a,b = Klass.instance, Klass.instance a == b # => true a.new # NoMethodError - new is private ..."
- !ruby/struct:SM::Flow::LI
label: "*"
body: ``The instance'' is created at instantiation time, in other words the first call of Klass.instance(), thus
- !ruby/struct:SM::Flow::VERB
body: " class OtherKlass\n include Singleton\n # ...\n end\n ObjectSpace.each_object(OtherKlass){} # => 0.\n"
- !ruby/struct:SM::Flow::LI
label: "*"
body: This behavior is preserved under inheritance and cloning.
type: :BULLET
- !ruby/struct:SM::Flow::P
body: This is achieved by marking
- !ruby/object:SM::Flow::LIST
contents:
- !ruby/struct:SM::Flow::LI
label: "*"
body: Klass.new and Klass.allocate - as private
type: :BULLET
- !ruby/struct:SM::Flow::P
body: Providing (or modifying) the class methods
- !ruby/object:SM::Flow::LIST
contents:
- !ruby/struct:SM::Flow::LI
label: "*"
body: Klass.inherited(sub_klass) and Klass.clone() - to ensure that the Singleton pattern is properly inherited and cloned.
- !ruby/struct:SM::Flow::LI
label: "*"
body: "Klass.instance() - returning ``the instance''. After a successful self modifying (normally the first) call the method body is a simple:"
- !ruby/struct:SM::Flow::VERB
body: " def Klass.instance()\n return @<em>instance</em>\n end\n"
- !ruby/struct:SM::Flow::LI
label: "*"
body: Klass._load(str) - calling Klass.instance()
- !ruby/struct:SM::Flow::LI
label: "*"
body: 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".
type: :BULLET
- !ruby/struct:SM::Flow::P
body: The instance method of Singleton are
- !ruby/object:SM::Flow::LIST
contents:
- !ruby/struct:SM::Flow::LI
label: "*"
body: clone and dup - raising TypeErrors to prevent cloning or duping
- !ruby/struct:SM::Flow::LI
label: "*"
body: _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''.
type: :BULLET
constants: []
full_name: Singleton
includes: []
instance_methods:
- !ruby/object:RI::MethodSummary
name: _dump
- !ruby/object:RI::MethodSummary
name: clone
- !ruby/object:RI::MethodSummary
name: dup
name: Singleton
superclass:
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