Why expressions doesn't support IdentityEquality?

Question

There is no IdentityEqual item in ExpressionType enumeration. How can I construct expreesion tree with VB.NET Is operator?

Answer 1

Have you tried using Expression.Equal, specifying the implementation to use?

In C#:

MethodInfo referenceEquality = typeof(object).GetMethod("ReferenceEquals",
    BindingFlags.Static | BindingFlags.Public);
Expression equality = Expression.Equal(lhs, rhs, true, referenceEquality);

Here's a complete example (again, C# - but you should be able to translate it easily):

using System;
using System.Reflection;
using System.Linq.Expressions;

class Test
{
    static void Main()
    {
        var lhs = Expression.Parameter(typeof(string), "lhs");
        var rhs = Expression.Parameter(typeof(string), "rhs");        
        MethodInfo referenceEquality = typeof(object).GetMethod
            ("ReferenceEquals", BindingFlags.Static | BindingFlags.Public);
        var equality = Expression.Equal(lhs, rhs, true, referenceEquality);
        var lambda = Expression.Lambda<Func<string, string, bool>>
            (equality, new[] { lhs, rhs });

        var compiled = lambda.Compile();

        string x = "hello";
        string y = x;
        string z = new string(x.ToCharArray());
        Console.WriteLine(compiled(x, y)); // True
        Console.WriteLine(compiled(x, z)); // False
    }
}