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