c# - Incorrect number of parameters supplied for lambda declaration

Question

Please have a look at my code: I'm trying to create myCar with an Expression Tree.

I get an ArgumentException on this line var m = Expression.Lambda<Func<Engine,... The message is Incorrect number of parameters supplied for lambda declaration.

public class Engine
{
    public string Name { get; private set; }
    public Engine(string name)
    {
        Name = name;
    }
}
public class Car
{
    private readonly Engine engine;
    public Car(Engine engine)
    {
        this.engine = engine;
    }
    public string GetEngineName(){return engine.Name;}
}
class Program
{
    static void Main(string[] args)
    {
        var ci = typeof (Car).GetConstructor(new[] {typeof (Engine)});

        var engine = Expression.Parameter(typeof (Engine));

        var m = Expression.Lambda<Func<Engine,Car>>(Expression.New(ci, engine))
                          .Compile();

        var myCar = m(new Engine("TDI 2.0"));
        var s = myCar.GetEngineName();
    }
}

I can't figure out what's wrong and where I did the error. Thanks in advance.

Answer 1

You must specify the engine in the 'params ParameterExpression[] parameters' part of Expression.Lambda

var m = Expression.Lambda<Func<Engine, Car>>(Expression.New(ci, engine), engine)