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Decorator Pattern in Go

This is the third chapter of the “Head First Design Patterns” book. I have covered the Strategy and Observer patterns before.

The problem

We are told to design an ordering application at a coffee shop. It sells a variety of beverages like

• House Blend
• Dark Roast
• Decaf
• Espresso

Apart from these, the customer has the choice to have condiments (add-ons) like

• Steamed milk
• Soy
• Mocha
• Whipped milk

Thought process

Approach 1

• What a noob coder like me would do is make an abstraction of Beverage, and derive concrete implementations of House Blend, Dark Roast, and so forth.
• The problem arises with the condiments, using the above approach we are spoiled with choices and our implementations become

House Blend with steamed milk and mocha

Dark Roast with whip and soy

• Just imagine the number of…