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Program Repair Shop

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Kinds of observers

• We'll say that an object (or class) has direct and class observers

• These groups overlap

• In this example, each class and object has exactly one direct observer

• $g1 and $g2 are class observers

• Alarm has one class observer ($g1) which is also its direct observer

• Alarm::Noisy has two class observers ($g1 and $g2)

• Only $g2 is a direct observer of Alarm::Noisy

• $a1 also has two class observers ($g1 and $g2)

• Its direct observer, $g3, is not a class observer

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