When I use Expression.Lambda( ... ).Compile()
in order to create a delegate from an expression tree, the result is a delegate of which the first argument is Closure
.
public static Func<T, T, T> CreateTest<T>()
{
ParameterExpression a = Expression.Parameter( typeof( T ) );
ParameterExpression b = Expression.Parameter( typeof( T ) );
Expression addition = Expression.Add( a, b );
return (Func<T, T, T>)Expression.Lambda( addition, a, b ).Compile();
}
...
// 'addition' equals
// Int32 lambda_method(
// System.Runtime.CompilerServices.Closure,
// Int32,
// Int32 )
Func<int, int, int> addition = DelegateHelper.CreateTest<int>();
int result = addition( 5, 5 );
I can easily call the delegate through ordinary code without passing a Closure
object, but where does this Closure
come from?
How can I call this delegate dynamically?
// The following does not work.
// Exception: MethodInfo must be a runtime MethodInfo object.
MethodInfo additionMethod = addition.Method;
int result = (int)additionMethod.Invoke( null, new object[] { 5, 5 } );
Using expression trees it looks like I have to pass the Closure
object.
PropertyInfo methodProperty
= typeof( Delegate ).GetProperty( "Method", typeof( MethodInfo ) );
MemberExpression getDelegateMethod
= Expression.Property( Expression.Constant( addition ), methodProperty );
Func<MethodInfo> getMethodInfo
= (Func<MethodInfo>)Expression.Lambda( getDelegateMethod ).Compile();
// Incorrect number of arguments supplied for call to method
// 'Int32 lambda_method(System.Runtime.CompilerServices.Closure, Int32, Int32)'
Expression call
= Expression.Call(
getMethodInfo(),
Expression.Constant( 5 ), Expression.Constant( 5 ) );
This is a simplified example which doesn't make sense in its own right. What I am actually trying to achieve is to be able to wrap e.g. Func<Action<SomeObject>>
with Func<Action<object>>
. I can already do this for non nested delegates. This is useful during reflection, as discussed here.
How should I correctly initialize this Closure
object, or how do I prevent it from being there?
See Question&Answers more detail:
os