TemplatePattern.md

The Template Pattern

C++ Project Example

Link: Coffee and Tea

Theory

The Template Method Pattern defines the skeleton of an algorithm in a method, deferring some steps to subclasses. Template Methods lets subclasses redefine certain steps fo an algorithm without changing the algorithm's structure.

What's a template? It's just a method that defines an algorithm as a set of steps.

classDiagram

class AbstractClass {
    templateMethod() // algorithm
    
    primitiveOperation1() // to be implemented by subclass
    primitiveOperation2() // to be implemented by subclass
    concreteOperation() 
    hook() // hook into algorithm
}

class ConcreteClass {
    primitiveOperation1()
    primitiveOperation2()
}

AbstractClass <|-- ConcreteClass

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• concrete operations: methods that are common in the algorithm
• primitive operations: methods that need to be modified/implemented by subclasses
• hooks: method that gives subclasses an ability to hook into the algorithm at various points; default implementation is provided by template method (look at the code example for a clear picture of what a hook does)

The Hollywood Principle

Don't call us, we'll call you.

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This principle gives us a way to prevent "dependency rot".

With this principle, we allow low-level components to hook themselves into a system, but the high-level components determine when they are needed, and how. In simpler words, the high-level components give the low-level components "don't call us we'll call you" treatment.

The template method call methods of its own and low-level components (subclasses).

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