![Original Problem code class Node (object): def __init__(self, name): self.name = name def toPlainTextString (self): return self.name class FormTag (Node): def __init__(self): self.allNodesVector = [] def toPlainTextString (self): result = "" for node in self.allNodesVector: result += node.toPlainTextString() return result class LinkTag (Node): def __init__(self): self.linkData = [] def toPlainTextString (self): result = "" for node in self.linkData: result += node.toPlainTextString() return result f = FormTag() f.allNodesVector.append(Node("a")) f.allNodesVector.append(Node("b")) f.allNodesVector.append(Node("c")) l = LinkTag() l.linkData += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString() abc xyz output](https://image.slidesharecdn.com/extract-composite-talk-andy-1205205635320634-2/85/Extract-Composite-Talk-Andy-6-320.jpg)
![Everything moved to Composite class Composite (Node): def __init__(self): self.children = [] def toPlainTextString(self): result = "" for node in self.children: result += node.toPlainTextString() return result class FormTag(Composite): pass class LinkTag(Composite): pass](https://image.slidesharecdn.com/extract-composite-talk-andy-1205205635320634-2/85/Extract-Composite-Talk-Andy-10-320.jpg)
![Step 4 Check interfaces so that client code using the old composites still works. f = FormTag() f. children .append(Node("a")) f. children .append(Node("b")) f. children .append(Node("c")) l = LinkTag() l. children += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString() f = FormTag() f. allNodesVector .append(Node("a")) f. allNodesVector .append(Node("b")) f. allNodesVector .append(Node("c")) l = LinkTag() l. linkData += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString()](https://image.slidesharecdn.com/extract-composite-talk-andy-1205205635320634-2/85/Extract-Composite-Talk-Andy-11-320.jpg)
Extract Composite Talk Andy
- 1. Andy Bulka Technical Director Austhink Software www.austhink.com March 2008 Refactoring to patterns…
- 2. Simple Composite pattern Class with a “children” collection Children are of type Node (i.e. you point to yourself)
- 3. Classic Composite pattern (GOF) Distinguish between Composites and Leaves Benefit of “classic” is that you can distinguish leafs and override display() or doubleClick() or whatever for leafs.
- 4. The Problem Code We have two classes that loop through their children – duplicate code The children attribute is named differently in both classes – inconsistent Both classes are “composites”
- 5. The Solution Create a common base class which has the generic “composite” looping behaviour That’s where the name of the refactoring comes from “Extract Composite”
- 6. Original Problem code class Node (object): def __init__(self, name): self.name = name def toPlainTextString (self): return self.name class FormTag (Node): def __init__(self): self.allNodesVector = [] def toPlainTextString (self): result = "" for node in self.allNodesVector: result += node.toPlainTextString() return result class LinkTag (Node): def __init__(self): self.linkData = [] def toPlainTextString (self): result = "" for node in self.linkData: result += node.toPlainTextString() return result f = FormTag() f.allNodesVector.append(Node("a")) f.allNodesVector.append(Node("b")) f.allNodesVector.append(Node("c")) l = LinkTag() l.linkData += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString() abc xyz output
- 7. Step 1 # Create a Composite Class - compile class Composite(Node): pass
- 8. Step 2 Make each child container (a class in the hierarchy that contains duplicate child-handling code) a subclass of your composite – compile class Composite(Node): pass class FormTag(Composite): … . class LinkTag(Composite): … .
- 9. Step 3 For each method with duplicated looping code 1. move & rename the child reference field UP to the composite using "Pull Up Field" 2. Move the method UP to the composite using "Pull Up Method" 3. Pull up any relevant constructor code too.
- 10. Everything moved to Composite class Composite (Node): def __init__(self): self.children = [] def toPlainTextString(self): result = "" for node in self.children: result += node.toPlainTextString() return result class FormTag(Composite): pass class LinkTag(Composite): pass
- 11. Step 4 Check interfaces so that client code using the old composites still works. f = FormTag() f. children .append(Node("a")) f. children .append(Node("b")) f. children .append(Node("c")) l = LinkTag() l. children += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString() f = FormTag() f. allNodesVector .append(Node("a")) f. allNodesVector .append(Node("b")) f. allNodesVector .append(Node("c")) l = LinkTag() l. linkData += [Node("x"), Node("y"), Node("z")] print f.toPlainTextString() print l.toPlainTextString()
- 12. New UML We have inserted a new class called Composite above the LinkTag and FormTag, which does the common looping work.
- 13. Before and After