Compare 2 lists, specifying the selectors as parameters

Question

I have the following function

public static class ListUtils
{
    public static bool ListsHaveCommonality<T>(List<T> listOne, List<T> listTwo, Func<T, string> selectorOne, Func<T, string> selectorTwo)
    {
    return listOne.Select(selectorOne).Intersect(listTwo.Select(selectorTwo)).Any();
    }
}

Then a test to check it works

//Arrange
List<Alias> aliases = new List<Alias>();
Alias a1 = new Alias { alias = "[email protected]" };
Alias a2 = new Alias { alias = "[email protected]" };
Alias a3 = new Alias { alias = "[email protected]" };

aliases.Add(a1);
aliases.Add(a2);
aliases.Add(a3);

List<string> chosenAliases = new List<string>
            {
                "[email protected]",
                "[email protected]",
            };

//Act
bool hasCommonality = ListUtils.ListsHaveCommonality(aliases, chosenAliases, (Alias a) => a.alias, (string s) => s);

//Assert
Assert.IsTrue(hasCommonality);

I get the following error

The type arguments for method System.Func, System.Func)' cannot be inferred from the usage. Try specifying the type arguments explicitly.

ListsHaveCommonality assumes that both lists have the same type parameter T. — Yacoub Massad
Oh yeah. That's helped me correct it to public static bool ListsHaveCommonality<T, T2>(List<T> listOne, List<T2> listTwo, Func<T, string> selectorOne, Func<T2, string> selectorTwo) — user2436996

Yacoub Massad Yacoub Massad · Accepted Answer · 2016-06-22T09:57:48

ListsHaveCommonality assumes that both lists have the same type parameter T. If you want to use it with lists that have different item types, you need to create a method that supports two type parameters like this:

public static class ListUtils
{
    public static bool ListsHaveCommonality<T1,T2>(
        List<T1> listOne,
        List<T2> listTwo,
        Func<T1, string> selectorOne,
        Func<T2, string> selectorTwo)
    {
        return listOne.Select(selectorOne).Intersect(listTwo.Select(selectorTwo)).Any();
    }
}

Compare 2 lists, specifying the selectors as parameters

2 Answers