IEnumerable Distinct comparer example

Question

I'm having trouble implementing an explicit comparer for the distinct method.

I have an expression defined in AddressResults that returns a list of address from an in-memory object list of type <Addresses>.    I want to return a distinct list of addresses

 

Here is some example code:

 

var results = (from p in AddressResults
                    select p).Distinct(new AddressComparer<Addresses>());

   public class AddressComparer : IEqualityComparer<Addresses>
    {
        public bool Equals(Tester x, Addresses y)
        {
            if (x.address == y.address && x.zip == y.zip)
                return true;
            return false;
        }

        public int GetHashCode(Addresses a)
        {
            string z = a.address+a.zip;
            return (z.GetHashCode());
        }
    }

I am getting a compile error:

The non-generic type AddressComparer  cannot be used with type arguments

on the var results... line. 

 

What am I doing wrong?

Answer 1

Jeff:

You've already specified the generic type parameter you need when you derived from IEqualityComparer<Addresses>. AddressComparer doesn't need a type param, so just remove the type param when you construct the comparer. For example:

var results = (from p in AddressResults
               select p).Distinct(new AddressComparer());

Hope that helps,

Answer 2

Hi there.
The compiler is right. You are creating an instance of a non generic type (AddressComparer) as if it is generic. Just Change this line of code:

Code Snippet

var results = (from p in AddressResults
                    select p).Distinct(new AddressComparer());

You also have a slight mistake in the Equal signature. The parameter x must be of type Addresses too.

Cheers.