4. Object Structures, Aliasing, and Encapsulation

More documents

Recommendations

Info

Desirable Aspects of Aliasing:• Consistent view to shared objects• Multiple cursors/iterators into object structures• Time and space efficiencyExamples:(Desirable aliasing)1. Address objects that capture the address of aperson or institution:- Several objects may reference an address A.- If A is modified, the referencing objects keepa consistent and up-to-date view.2. Consider a complex tree or graph structure:- The structure can be traversed byseveral iterators.- Cursors can point to nodes of current interest.3. Data structures can share objects (e.g. singlylinked lists):- avoids to copy data structures when they areenlarged or reduced in size;- saves a lot of memory space.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern6
Undesirable Aspects of Aliasing:1. Side-effects may become difficult to understandand control2. Inconsistent access to objects3. Aliases allow to by-pass interface operations4. Optimizations and formal techniques becomemore complexExamples:(Undesirable aliasing)1. Violation of invariants through aliases:- A set class uses a list class to implement thecollection. Invariant: no duplicates.- Alias to the list can lead to invariant violation.2. Inconsistent access:- An algorithm reads in different steps theattributes of an address object X (name,street, town).- Someone else modifies X while the algorithmreads its information.13.05.13© A. Poetzsch-Heffter, TU Kaiserslautern7
Page 1 and 2: 4. Object Structures, Aliasing,and
Page 3 and 4: Examples:(Object structures)1. A ve
Page 5: Problems:• Structural integrity (
Page 9 and 10: Forms of Alias Creation:Capturing:
Page 11 and 12: General approaches to solve alias p
Page 13 and 14: Examples:1. Immutable class:(Immuta
Page 15 and 16: class NotImmutableList extends Immu
Page 17 and 18: 4. Immutable objects with varying I
Page 19 and 20: 4.3 Alias Control and Encapsulation
Page 21 and 22: Roles in Object Structures:• Inte
Page 23 and 24: 2. Representations (rep mode):• E
Page 25 and 26: Meaning of alias modes:• Alias mo
Page 27 and 28: Programming Discipline (simplified)
Page 29 and 30: Example:(Representation exposure)-
Page 31 and 32: 4.3.2 Type-based EncapsulationType
Page 33 and 34: Connection with type systems:• Ea
Page 35 and 36: Scenarios in which references are i
Page 37 and 38: Remark:• The behavior of anonymou
Page 39 and 40: Further Structuring Techniques:Diff
Page 41 and 42: Cluster:Let G be the undirected gra
Page 43 and 44: Ownership:Idea:• Introduce an own
Page 45: The ownership relation is a binary

4. Object Structures, Aliasing, and Encapsulation

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?