189. this Pointer

Question.5

A developer registers a C++ object method as an RTOS callback:

class Button {
public:
   void onClick() { toggle_led(); }

   static void isr_wrapper(void* ctx) {
       static_cast<Button*>(ctx)->onClick();
   }

   void register_isr() {
       attach_interrupt(PIN_5, isr_wrapper, this);
   }
};

Why is this passed as the void* context?

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this is required for all interrupt handlers
The static wrapper receives this as void* context, casts it back to Button*, and calls the member function -- this bridges C-style callbacks to C++ object methods
this makes the callback faster
Without this, the interrupt handler cannot access GPIO registers

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