Software Design/Extract Wrapper Object

Extract Wrapper Object is a refactoring primarily aiming at removing logic duplication in the code as per DRY principle. Extract Wrapper Object is related to Extract Class and Introduce Parameter Object refactorings.

Examples

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If there is some code working with coordinates x and y and repeatedly performing operations such as negation:

x = -x
y = -y

The coordinates could be grouped into a Point object on which negate() function can be defined:

data class Point(var x: Double, var y: Double) {
    fun negate() {
        x = -x
        y = -y
    }
}

For another example, there may be a class with several operations and in some cases some aspect should be attached to calling those operations, such as logging or notifying some listener:

class Container {
  fun add(elem: Element) { ... }
  fun remove(elem: Element) { ... }
}

// Code repeated in multiple places within some other class:
container.add(elem)
listener.notifyAdded(elem)

// ...
container.remove(elem)
listener.notifyRemoved(elem)

Then a decorator class such as ListeneableContainer can be extracted to gather the repetition of the aspect's logic in one place:

class ListeneableContainer(val container: Container, val listener: Listener) {
  fun add(elem: Element) {
    container.add(elem)
    listener.notifyAdded(elem)
  }
  
  fun remove(elem: Element) {
    container.remove(elem)
    listener.notifyRemoved(elem)
  }
}

Why not

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Sources

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