Question

I’m trying to learn expressions, and I cannot find how to get the member type of a property in a expression. For example, consider this method:

static IEnumerable<Y> Filter<X,Y>(this IEnumerable<Person> p,  Expression<Func<Person,X>> select,  Expression<Func<X, Y>> format)
{
    foreach (var item in p)
    {
        // member name
        var m = ((MemberExpression)select.Body).Member;

        // member attributes
        var attributes = m.GetCustomAttributes(false);

        // member type?

        var a = select.Compile().Invoke(item);
        var b = format.Compile().Invoke(a);
        m.ToString();
        yield return b;
    }
}

It doesn’t do anything interesting, it is just for trying. If I do:

String y = _persons.Filter(p => p.DateOfBirth, d => d.ToString("yyyy")).ToArray().Single();

I can get in Y the year of the person in the collection. I want to know the type of “p.DateOfBirth” in the “Filter” method. How could I do that without using reflection?

Regards.

Answer 1

Assuming I’ve understood you correctly, you just need the Expression.Type property:

using System;
using System.Linq.Expressions;

class Person
{
    public DateTime DateOfBirth { get; set; }
}

public class Test
{
    static void Main()
    {
        Expression<Func<Person, DateTime>> expression = p => p.DateOfBirth;

        MemberExpression memberExpression = (MemberExpression) expression.Body;
        Console.WriteLine(memberExpression.Type); // Prints System.DateTime
    }    
}