How to cast Expression> to Expression>

Question

I\'ve been searching but I can\'t find how to cast from the type

Expression>

to the type:

Exp         


        

Answer 1

You can't just cast between them, as they're not the same kind of thing. However, you can effectively add a conversion within the expression tree:

using System;
using System.Linq.Expressions;

class Test
{
    // This is the method you want, I think
    static Expression> AddBox
        (Expression> expression)
    {
        // Add the boxing operation, but get a weakly typed expression
        Expression converted = Expression.Convert
             (expression.Body, typeof(object));
        // Use Expression.Lambda to get back to strong typing
        return Expression.Lambda>
             (converted, expression.Parameters);
    }

    // Just a simple demo
    static void Main()
    {
        Expression> x = text => DateTime.Now;
        var y = AddBox(x);        
        object dt = y.Compile()("hi");
        Console.WriteLine(dt);
    }        
}