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PH page 18-24 GoF Singleton p. 127-134

PH page 18-24 GoF Singleton p. 127-134. Emanuel Ekstrom. Orphans & Adoption. Context: Making a file system. Three objects: Node, File, Directory. Why do we need to adopt? Why do we need to orphan? Who gets an adopt/orphan interface? So are they all the same?. Singleton. Intent:

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PH page 18-24 GoF Singleton p. 127-134

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  1. PH page 18-24GoF Singleton p. 127-134 Emanuel Ekstrom

  2. Orphans & Adoption • Context: Making a file system. Three objects: Node, File, Directory. • Why do we need to adopt? • Why do we need to orphan? • Who gets an adopt/orphan interface? • So are they all the same?

  3. Singleton • Intent: ”Ensure a class only has one instance, and provide a global point of access to it.”

  4. Discussion • Who needs only one instance? • What is good about a global access point? • Why not global variables instead?

  5. How do we make a Singleton? (GoF p. 131) • Constructor protected • Public static Instance() function. • Is this enough?

  6. Discussion • What if we want to delete a Singleton? • What if a deleted Singleton is called? • Is there a solution to the problem?

  7. Subclassing • Problem: Making sure the subclasses are unique and that the clients can access it. • How is this solved? • Drawbacks?

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