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

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

• Emanuel Ekstrom

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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?

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Singleton

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

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Discussion

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

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How do we make a Singleton? (GoF p. 131)

• Constructor protected
• Public static Instance() function.
• Is this enough?

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Discussion

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

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Subclassing

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