MemberExpression: InvalidOperationExpression variable 'x' referenced from scope '', but it is not defined

Question

I\'m using System.Linq.Expressions

I was attempting to build a simple LambdaExpression that includes a MemberExpression. If I create the MemberExpression explicitly

Answer 1

You're creating different parameters called "x" several times. If you use a single ParameterExpression, it should all work fine.

ParameterExpression p = Expression.Parameter(typeof(Customer), "x");
MemberExpression m = Expression.MakeMemberAccess(p, 
    typeof(Customer).GetProperty("Title"));
expression2 = Expression.Lambda<Func<Customer, string>>(m, p);

m = Expression.Property(p, "Title");
expression3 = Expression.Lambda<Func<Customer, string>>(m, p);

fn = expression3.Compile();
fn = expression2.Compile();

Basically parameter expressions aren't matched by name - you've got to use the same one everywhere. It's a bit of a pain, but there we go...