Created
October 12, 2018 02:04
-
-
Save iknowcodesoup/2a8862ae84d9929adb51a715b1225635 to your computer and use it in GitHub Desktop.
dont-use-activator-createinstance-or-constructorinfo-invoke-use-compiled-lambda-expressions
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
namespace SView.Global | |
{ | |
using System; | |
using System.Linq.Expressions; | |
using System.Reflection; | |
/// <summary> | |
/// https://vagifabilov.wordpress.com/2010/04/02/dont-use-activator-createinstance-or-constructorinfo-invoke-use-compiled-lambda-expressions/ | |
/// </summary> | |
public class Activator | |
{ | |
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 | |
var compiled = (ObjectActivator<T>)lambda.Compile(); | |
return compiled; | |
} | |
} | |
} |
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment