Design Pattern: Iterator (Behavioural)
Intent: Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation [1]. This design pattern is also known as Cursor.
Motivation: An example of an aggregate object is an instance of the List ADT. Consequently, an iterator can be used to traverse the elements of a list with a set of high-level abstract operations. These operations may be implemented within the List ADT but as Gamma et al.[1] wonderfully puts it, the key idea in this pattern is to take the responsibility for access and traversal out of the list object and put it into an iterator object - given the iterator describes behaviour whilst the list describes a collection.
Implementation: The Iterator abstract class is used purely to specify the requirements of its concrete implementation. This abstraction could be implemented as an external/active or internal/passive iterator -
External := the onus is on the client to advance the traversal and request next elements.
Internal := the client can supply an operation to the iterator to perform over every element of a collection
Refer to pp.257-271 Gamma et al.[1] for more information on the Iterator (Behavioural) Design Pattern.
Written by Bobby Nedelkovski
MathWorks Australia
Copyright 2009-2010, The MathWorks, Inc.
Reference:
[1] Gamma, E., Helm, R., Johnson, R. and Vlissides, J. Design Patterns : Elements of Reusable Object-Oriented Software. Boston: Addison-Wesley, 1995.
Cite As
Bobby Nedelkovski (2024). Design Pattern: Iterator (Behavioural) (https://www.mathworks.com/matlabcentral/fileexchange/25225-design-pattern-iterator-behavioural), MATLAB Central File Exchange. Retrieved .
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Acknowledgements
Inspired by: Data Structure: A Cell Array List Container
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Version | Published | Release Notes | |
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1.5.0.1 | Updated license |
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1.5.0.0 | Allow creation of N-D arrays of CellArrayListIterators - this is due to the changes in CellArrayList (see File Exchange item #25024). UML Diagram has been updated to reflect the change. |
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1.3.0.0 | Abstract properties in abstract classes List and Iterator changed to concrete protected - conforms with R2009b OOP. Updated UML diagram to reflect this change. Bug fix with remove() method in CellArrayList. |
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1.2.0.0 | Removed details on the implementation from the 'Description' field as this can be found in 'CellArrayListIterator.m' and included references to the files of interest. |
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1.0.0.0 |