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May 12, 2023

The Factory Method is just an implementation of the Template Method but for building objects.

Let us consider an IRL example, I’ve recently coded. Here’s the story: I was building and HD44780 LCD driver. I needed some hardware abstraction, so that I could test the rest of the software without any running hardware. Also, I didn’t know if I would bit-bang my way through, or use some funky I2C IO expander as a proxy.

Depending on my project configuration, I needed an LCD driver:

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struct ILcdDriver{
	//...
	virtual void sendCmd(char cmd) = 0;
	virtual void sendData(char data) = 0;
};

The actual drivers in question would be:

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struct MockLcdDriver: ILcdDriver {};

struct GpoLcdDriver: ILcdDriver{};

struct ProxyLcdDriver: ILcdDriver{};

Each one behaving totally differently but giving the same end result: controlling the HD44780 (or pretending) in a proper way.

Now I needed an entity that would deliver me a proper driver, depending on the given project configuration.

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struct IDeliverLcdDriver{
	// ...
	virtual ILcdDriver* deliver() = 0;
};

Now defining classes:

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struct DeliverMockLcdDriver:IDeliverLcdDriver{};

struct DeliverGpoLcdDriver:IDeliverLcdDriver{};

struct DeliverProxyLcdDriver:IDeliverLcdDriver{};

I could easily generate drivers based even on #ifdef’s"

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// somewhere in the init part of the project
ILcdDriver *drv = nullptr;

IDeliverLcdDriver *deliver = nullptr;

#if defined(LCD_GPO)
	deliver = new DeliverGpoLcdDriver;
#elif defined(LCD_PROXY)
	deliver = new DeliverProxyLcdDriver;
#else
	deliver = new DeliverMockLcdDriver;
#endif

drv = deliver->deliver();

// ...

➡️ Clean code guidelines for intermediate developers: A roadmap

⬅️ Composite design pattern

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