Podcast
Questions and Answers
What does the open-closed principle state about software entities?
What does the open-closed principle state about software entities?
- They should be closed for extension and modification.
- They should be completely independent of changes.
- They should be open for modification but closed for extension.
- They should be open for extension and closed for modification. (correct)
What is a consequence of violating the open-closed principle in software design?
What is a consequence of violating the open-closed principle in software design?
- The program may become fragile, rigid, and unpredictable. (correct)
- The program becomes more flexible and adaptable to change.
- The program becomes more reusable with fewer changes needed.
- The program easily integrates new modules without issues.
According to Bertrand Meyer, how should systems be designed to cope with changes over time?
According to Bertrand Meyer, how should systems be designed to cope with changes over time?
- By ensuring modules never change. (correct)
- By implementing extensive runtime type identification.
- By frequently modifying existing modules.
- By encouraging the use of global variables.
Which heuristic is associated with the open-closed principle?
Which heuristic is associated with the open-closed principle?
What type of approach does the open-closed principle advocate for when requirements change?
What type of approach does the open-closed principle advocate for when requirements change?
The principle that allows the behavior of a module to be extended while keeping its source code inviolate is known as the ______ principle.
The principle that allows the behavior of a module to be extended while keeping its source code inviolate is known as the ______ principle.
In C++, abstractions are created using abstract base classes, which represent an unbounded group of possible ______.
In C++, abstractions are created using abstract base classes, which represent an unbounded group of possible ______.
A module that is closed for modification typically has a fixed ______.
A module that is closed for modification typically has a fixed ______.
Creating new derivative classes allows a module to extend its behavior while still depending on an ______ that is fixed.
Creating new derivative classes allows a module to extend its behavior while still depending on an ______ that is fixed.
In a design that conforms to the open-closed principle, the ______ class is an abstract class with pure-virtual member functions.
In a design that conforms to the open-closed principle, the ______ class is an abstract class with pure-virtual member functions.
Flashcards
Open-Closed Principle
Open-Closed Principle
Software entities should be designed to be expandable without altering existing code.
Software Entities (Classes)
Software Entities (Classes)
Components of a software system, like classes, modules, and functions.
Closed for Modification
Closed for Modification
Existing code should not be changed when extending functionality.
Open for Extension
Open for Extension
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Fragile Design
Fragile Design
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Abstract Base Class (ABC)
Abstract Base Class (ABC)
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Why are ABCs important for the Open-Closed Principle?
Why are ABCs important for the Open-Closed Principle?
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Study Notes
The Open-Closed Principle
- This principle is a software engineering guideline for designing software
- It states that software entities (like classes, modules, and functions) should be open for extension but closed for modification
- This means that new functionality can be added without altering existing code
- Changes in requirements should be accommodated by adding new code, not by altering existing code
- This approach leads to more stable, maintainable, and reusable software
- Avoid cascading changes to dependent modules when making a single change
Software Design Heuristics
- All member variables should be private
- Global variables should be avoided
- Avoid using run time type identification (RTTI)
Open vs Closed Modification
- Open for Extension: The software should be designed in such a way that it can be easily extended to incorporate new functionalities without having to change the existing code structure.
- Closed for Modification: Modifications to existing code that could potentially break existing functionality should be avoided
- Designers should anticipate future changes when creating software, while maintaining existing functionality.
The Shape Abstraction
- Using procedural techniques for a shape drawing application results in code that needs modification to support different kinds of shapes
- Using an object-oriented approach, using an abstract class as a base class (Shape) and deriving circle and square classes from it leads to easier and expandable code.
Abstraction as a Key to Open-Closed Principles
- Abstractions can be fixed representations of unbounded possible behaviors.
- Abstractions are abstract base classes
- The different possible behaviors are represented by the different derivative classes that can extend the original abstraction.
Strategic Closure
- Complete closure is not possible in large software projects
- The focus needs to be on strategic closure, meaning anticipating the most probable changes when designing software and creating the necessary abstractions.
- Using ordering abstractions to close DrawAllShapes against changes in the ordering of drawing shapes
- Using a table-driven approach (Listing 6) to add more robust ordering mechanisms for shapes.
Heuristics and Conventions
- Make all member variables private to avoid unintended modifications of data and potential software instability.
- Avoid global variables as much as possible, as this can lead to a domino effect of code changes throughout.
- Be cautious with run-time type identification (RTTI) to avoid unnecessary and potential unintended breakage if not careful.
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