ParameterExpression to Object Casting with Reflection

Question

I want to cast any object from ParameterExpression class.

This is sample code (and pseudo what i want to say) :

public void Execute(Expression<Action<TService>> operation) { try { var param = operation.Parameters[0]; //myparameter to cast var obj = param as AnyCastObject; // I want to cast DoSomething(obj); // and do something this object without losing any assigned propery. operation.Compile().Invoke(OpenNewChannel); } finally { CloseChannel(); } }

Edit:

This is my method body:

Execute(x => x.UserAuthentication(requestDto));

I want to manipulate requestDto.

You don't seem to comprehend how expressions work. param isn't the "value" of the parameter, it is a "parameter" in the sense "the descriptor of the parameter". "casting" the "descriptor of the parameter" doesn't have any sense. What you can do is create a new expression tree where the "value" of the parameter is casted to something else and then something is done. — xanatos
– xanatos, Commented Mar 31, 2015 at 9:08
I know param is not a value. I write this sample for pseudo that what i want yo say. But i dont understand what your saying. — Oğuzhan Soykan
– Oğuzhan Soykan, Commented Mar 31, 2015 at 9:32
So what do you want to cast? Do you want to have a "new" ParameterExpression for a different type (MyService instead of TService)? Do you want to change the parameter type of the operation from TService to MyService? Or what? — xanatos
– xanatos, Commented Mar 31, 2015 at 9:35
And when you operation.Compile(), do you want to compile the operation that was passed or do you want to compile an operation that you modified in some way? — xanatos
– xanatos, Commented Mar 31, 2015 at 9:36
In fact i want to copy or extract parameter before invoking. İf i want to create new instance of parameter then i use Activator.CreateInstance. But i dont want New instance i want to reference current instance parameter which passing to expression. — Oğuzhan Soykan
– Oğuzhan Soykan, Commented Mar 31, 2015 at 10:09

xanatos · Accepted Answer · 2015-03-31 10:30:16Z

Here it is... With this you should be able to extract your requestDto.

Note that you don't need the Invoke() when you call compiled expressions.

operation.Compile()(OpenNewChannel);

is enough.

Now, to extract the requestDto:

// Works for Execute(x => x.UserAuthentication(something)) // where something must be a constant value, a variable, // a field, a property var param = operation.Parameters[0]; //myparameter to cast var body = operation.Body as MethodCallExpression; if (body == null || body.Object != param || body.Method.Name != "UserAuthentication") { throw new NotSupportedException(); } // If you have a type for the parameter, replace it here: // object -> yourtype object requestValue; var constantExpression = body.Arguments[0] as ConstantExpression; if (constantExpression == null) { // For nearly all the types of expression, the only way // to extract the final value is to compile them and then // execute them (the execution is the last "()" ) // If you have a type for the parameter, replace it here: // Func<object> -> Func<yourtype> requestValue = Expression.Lambda<Func<object>>(body.Arguments[0]).Compile()(); } else { // Constant expression values can be directly extracted // If you have a type for the parameter, replace it here: // (yourtype)constantExpression.Value requestValue = constantExpression.Value; }

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