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86 lines
2.6 KiB
ReStructuredText
86 lines
2.6 KiB
ReStructuredText
`Memento`__
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===========
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Purpose
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-------
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It provides the ability to restore an object to it's previous state (undo
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via rollback) or to gain access to state of the object, without revealing
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it's implementation (i.e., the object is not required to have a function
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to return the current state).
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The memento pattern is implemented with three objects: the Originator, a
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Caretaker and a Memento.
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Memento – an object that *contains a concrete unique snapshot of state* of
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any object or resource: string, number, array, an instance of class and so on.
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The uniqueness in this case does not imply the prohibition existence of similar
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states in different snapshots. That means the state can be extracted as
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the independent clone. Any object stored in the Memento should be
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*a full copy of the original object rather than a reference* to the original
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object. The Memento object is a "opaque object" (the object that no one can
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or should change).
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Originator – it is an object that contains the *actual state of an external
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object is strictly specified type*. Originator is able to create a unique
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copy of this state and return it wrapped in a Memento. The Originator does
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not know the history of changes. You can set a concrete state to Originator
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from the outside, which will be considered as actual. The Originator must
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make sure that given state corresponds the allowed type of object. Originator
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may (but not should) have any methods, but they *they can't make changes to
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the saved object state*.
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Caretaker *controls the states history*. He may make changes to an object;
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take a decision to save the state of an external object in the Originator;
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ask from the Originator snapshot of the current state; or set the Originator
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state to equivalence with some snapshot from history.
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Examples
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--------
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- The seed of a pseudorandom number generator
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- The state in a finite state machine
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- Control for intermediate states of `ORM Model <http://en.wikipedia.org/wiki/Object-relational_mapping>`_ before saving
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UML Diagram
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-----------
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.. image:: uml/uml.png
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:alt: Alt Momento UML Diagram
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:align: center
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Code
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----
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You can also find this code on `GitHub`_
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Memento.php
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.. literalinclude:: Memento.php
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:language: php
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:linenos:
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State.php
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.. literalinclude:: State.php
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:language: php
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:linenos:
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Ticket.php
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.. literalinclude:: Ticket.php
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:language: php
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:linenos:
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Test
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----
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Tests/MementoTest.php
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.. literalinclude:: Tests/MementoTest.php
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:language: php
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:linenos:
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.. _`GitHub`: https://github.com/domnikl/DesignPatternsPHP/tree/main/Behavioral/Memento
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.. __: http://en.wikipedia.org/wiki/Memento_pattern
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