Created
December 17, 2015 08:53
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Object Activator / Build Instance Factory Delegate
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using System; | |
using System.Reflection; | |
using System.Linq.Expressions; | |
using System.Collections; | |
using System.Linq; | |
public class Program | |
{ | |
public static void Main() | |
{ | |
var factory = ActivatorEx.CreateInstanceFactoryDelegate<Hello>(); | |
factory("hello", 777); | |
typeof(Hello).CreateFactory<Hello>().Invoke("hello",888); | |
} | |
} | |
public class Hello | |
{ | |
public Hello(string greetMessage, int age) | |
{ | |
Console.WriteLine(greetMessage + age.ToString()); | |
} | |
} | |
public static class ActivatorEx | |
{ | |
public delegate T ObjectActivator<T>(params object[] args); | |
public static ObjectActivator<T> GetActivator<T>(ConstructorInfo ctor) | |
{ | |
Type type = ctor.DeclaringType; | |
ParameterInfo[] paramsInfo = ctor.GetParameters(); | |
//create a single param of type object[] | |
ParameterExpression param = Expression.Parameter(typeof (object[]), "args"); | |
Expression[] argsExp = new Expression[paramsInfo.Length]; | |
//pick each arg from the params array | |
//and create a typed expression of them | |
for (int i = 0; i < paramsInfo.Length; i++) | |
{ | |
Expression index = Expression.Constant(i); | |
Type paramType = paramsInfo[i].ParameterType; | |
Expression paramAccessorExp = Expression.ArrayIndex(param, index); | |
Expression paramCastExp = Expression.Convert(paramAccessorExp, paramType); | |
argsExp[i] = paramCastExp; | |
} | |
//make a NewExpression that calls the | |
//ctor with the args we just created | |
NewExpression newExp = Expression.New(ctor, argsExp); | |
//create a lambda with the New | |
//Expression as body and our param object[] as arg | |
LambdaExpression lambda = Expression.Lambda(typeof (ObjectActivator<T>), newExp, param); | |
//compile it | |
ObjectActivator<T> compiled = (ObjectActivator<T>)lambda.Compile(); | |
return compiled; | |
} | |
public static ObjectActivator<T> CreateInstanceFactoryDelegate<T>() | |
{ | |
ConstructorInfo ctor = typeof (T).GetConstructors().First(); | |
ObjectActivator<T> createdActivator = GetActivator<T>(ctor); | |
return createdActivator; | |
} | |
public static ObjectActivator<T> CreateFactory<T>(this Type t){ | |
return CreateInstanceFactoryDelegate<T>(); | |
} | |
} |
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