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natebosch/_refactoring_inheritance.md

Last active April 3, 2016 22:10
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_refactoring_inheritance.md

Improving on the refactoring in the clean code talk on inheritance, polymorphism, and testing by going from an inheritance approach to a composition approach.

Files should be read in order switch -> inheritance -> composition.

Raw
composition_version.dart
void main() {
var root = new OpNode(add, new ValueNode(1),
new OpNode(multiply, new ValueNode(2), new ValueNode(3)));
print(root.toString());
print('=');
print(root.evaluate());
}
final multiply = new Multiplication();
final add = new Addition();
abstract class Operation {
num evaluate(num left, num right);
}
class Multiplication implements Operation {
num evaluate(num left, num right) => left * right;
String toString() => '*';
}
class Addition implements Operation {
num evaluate(num left, num right) => left + right;
String toString() => '+';
}
abstract class Node {
num evaluate();
}
class ValueNode implements Node {
final num value;
ValueNode(this.value);
num evaluate() => value;
String toString() => value.toString();
}
class OpNode implements Node {
final Operation operation;
final Node left;
final Node right;
OpNode(this.operation, this.left, this.right);
num evaluate() => operation.evaluate(left.evaluate(), right.evaluate());
String toString() => '$left $operation $right';
}
Raw
inheritance_version.dart
void main() {
var root = new AdditionNode(new ValueNode(1),
new MultiplicationNode(new ValueNode(2), new ValueNode(3)));
print(root.toString());
print('=');
print(root.evaluate());
}
abstract class Node {
num evaluate();
}
class ValueNode extends Node {
final num value;
ValueNode(this.value);
num evaluate() => value;
String toString() => value.toString();
}
abstract class OpNode extends Node {
final Node left;
final Node right;
OpNode(this.left, this.right);
}
class AdditionNode extends OpNode {
AdditionNode(Node left, Node right) : super(left, right);
num evaluate() => left.evaluate() + right.evaluate();
String toString() => '$left + $right';
}
class MultiplicationNode extends OpNode {
MultiplicationNode(Node left, Node right) : super(left, right);
num evaluate() => left.evaluate() * right.evaluate();
String toString() => '$left * $right';
}
Raw
switch_version.dart
void main() {
var root = new Node(
'+',
0,
new Node('#', 1, null, null),
new Node(
'*', 0, new Node('#', 2, null, null), new Node('#', 3, null, null)));
print(root.toString());
print('=');
print(root.evaluate());
}
class Node {
final char operator;
final num value;
final Node left;
final Node right;
Node(this.operator, this.value, this.left, this.right);
num evaluate() {
switch (operator) {
case '#':
return value;
case '+':
return left.evaluate() + right.evaluate();
case '*':
return left.evaluate() * right.evaluate();
}
}
String toString() {
switch (operator) {
case '#':
return '$value';
case '+':
return '$left + $right';
case '*':
return '$left * $right';
}
}
}
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