72. mutable Keyword

Question.4

A developer marks a critical member as mutable to avoid fixing a design issue:

class Motor {
   mutable int speed;  // Marked mutable to allow modification everywhere
public:
   void update() const { speed = 100; } // Should not be const!
};

Is this good use of mutable?

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Yes -- mutable allows flexible access
No -- speed is the core logical state of the Motor; making it mutable defeats const-correctness and hides a design error (update should not be const)
Yes -- as long as it works, design does not matter
No -- but only because Motor is a hardware class

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