I discovered in my code a redundant pattern :
private SomeType _something; private SomeType something { get { if (_something == null) _something = new SomeType(....); return _something;} } |
Usefull in Silverlight, when your Blender always say “Can’t compile ! Strange errors ! but compiles when i comment your WebClient… in ctor of that class…”
So i use it to have members builded the first time they are used, “Just in time”.
/!\ It’s not a Singleton ! i can have others instance of this class new-ing it directly !
/!\ Singleton is Evil // feed the Troll
So i factorized it :
public class Jit<T> { T _instance; object[] _ctor_params; public Jit(object[] ctor_params) { _ctor_params = ctor_params; } public Jit() { } public T create(object[] ctor_params) { Type[] param_types = ctor_params.Aggregate<object, List<Type>>( new List<Type>(), (List<Type> lt, object o) => { lt.Add(o.GetType()); return lt; }).ToArray(); var ctor = typeof(T).GetConstructor(param_types); if (ctor == null) throw new Exception(param_types.Aggregate<Type, String>( "No constructor found for " + typeof(T).Name + " taking", (string i, Type t) => { return i + " " + t.Name; })); return (T)ctor.Invoke(_ctor_params); } public T create() { return (_ctor_params == null) ? create(new object[] { }) : create(_ctor_params); } public T single() { if (_instance == null) _instance = create(); return _instance; } } |
A usage demo :
public class Test { Test(string foo, int bar) { Console.WriteLine("Test ctor with : " + foo + " and " + bar); } public void foo() { Console.WriteLine("bar"); } } public partial class Page : UserControl { public event EventHandler my_event; private Jit<Test> test = new Jit<Test>(new object[]{"42", 42}); public Page() { InitializeComponent(); // test is not yet built test.single().foo(); // Whill build a Test and call foo() test.single().foo(); // Whill call foo on the same Test. } } |
So a :
private SomeType _something; private SomeType something { get { if (_something == null) _something = new SomeType(....); return _something;} } |
became :
private Jit<SomeType> something = new Jit<SomeType>(new object[]{...}); |
Note the Jit ctor, taking a array of objects, it’s the objects to pass to your ctor’s class (found by reflection using their types)