Unity implements design patterns - interpreter mode
Interpreter Pattern is a mode that parses according to prescribed grammar, and is rarely used in real projects. Given a language, define a representation of its grammar, and define an interpreter that uses that representation to interpret sentences in the language.
Here's an example to demonstrate: Convert Roman text to decimal format
1.Context
class Context
{
private string _input;
private int _output;
// Constructor
public Context(string input)
{
this._input = input;
}
// Gets or sets input
public string Input
{
get {
return _input; }
set {
_input = value; }
}
// Gets or sets output
public int Output
{
get {
return _output; }
set {
_output = value; }
}
}
2.Expression
Interpreter base class
abstract class Expression
{
//"MCMXXVIII";
public void Interpret(Context context)
{
if (context.Input.Length == 0)
return;
if (context.Input.StartsWith(Nine()))
{
context.Output += (9 * Multiplier());
context.Input = context.Input.Substring(2);
}
else if (context.Input.StartsWith(Four()))
{
context.Output += (4 * Multiplier());
context.Input = context.Input.Substring(2);
}
else if (context.Input.StartsWith(Five()))
{
context.Output += (5 * Multiplier());
context.Input = context.Input.Substring(1);
}
while (context.Input.StartsWith(One()))
{
context.Output += (1 * Multiplier());
context.Input = context.Input.Substring(1);
}
}
public abstract string One();
public abstract string Four();
public abstract string Five();
public abstract string Nine();
public abstract int Multiplier();
}
3.ThousandExpression
Thousands Digits Interpreter
class ThousandExpression : Expression
{
public override string One() {
return "M"; }
public override string Four() {
return " "; }
public override string Five() {
return " "; }
public override string Nine() {
return " "; }
public override int Multiplier() {
return 1000; }
}
4.HundredExpression
Hundreds digit interpreter
class HundredExpression : Expression
{
public override string One() {
return "C"; }
public override string Four() {
return "CD"; }
public override string Five() {
return "D"; }
public override string Nine() {
return "CM"; }
public override int Multiplier() {
return 100; }
}
5.TenExpression
Ten digit interpreter
class TenExpression : Expression
{
public override string One() {
return "X"; }
public override string Four() {
return "XL"; }
public override string Five() {
return "L"; }
public override string Nine() {
return "XC"; }
public override int Multiplier() {
return 10; }
}
6.OneExpression
single digit interpreter
class OneExpression : Expression
{
public override string One() {
return "I"; }
public override string Four() {
return "IV"; }
public override string Five() {
return "V"; }
public override string Nine() {
return "IX"; }
public override int Multiplier() {
return 1; }
}
7.Testing
public class InterpreterExample1 : MonoBehaviour
{
void Start()
{
string roman = "MCMXXVIII";
Context context = new Context(roman);
// Build the 'parse tree'
List<Expression> tree = new List<Expression>();
tree.Add(new ThousandExpression());
tree.Add(new HundredExpression());
tree.Add(new TenExpression());
tree.Add(new OneExpression());
// Interpret
foreach (Expression exp in tree)
{
exp.Interpret(context);
}
Debug.Log(roman+" = "+ context.Output);
}
}