Singleton

Description

• Provide single entry point to global variable

• It is a global variable

• Only more engineered

Drawbacks

• Hidden dependencies

• Instantiation should be automatic

• … and this is where the problems arise

Exercises

• Exercise: Singleton (Flexible)

• Exercise: Singleton (Flexible And Strict)

• Exercise: Singleton (Inflexible)

And class Person?

Imagine a system with huge numbers of instances of

class Person
{
public:
    // ...
    void be_sick();   // <--- charges social insurance. which one?
    // ...
};

• Do all Person instance share the same insurance institution? Which one?

• How to test such a system? Provide a test case fixture to setup and teardown the singleton instance?