PH page 18-24GoF 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:

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

Discussion

Who needs only one instance?

What is good about a global access point?

Why not global variables instead?

How do we make a Singleton? (GoF p. 131) Constructor protected Public static Instance() function.

Is this enough?

Discussion

What if we want to delete a Singleton?

What if a deleted Singleton is called?

Is there a solution to the problem?

Subclassing

Problem: Making sure the subclasses are unique and that the clients can access it.

How is this solved?

Drawbacks?