包含使用Linq / Lambda的方法

Question

This method finds different dates and adds to dates array. Is it possible to make this method with linq/lambda?

public static void FindDates(DateTime[] dates, LinkedList<Letter> L, out int counter)
{
    counter = 0;

    foreach (var let in L)
    {
        if (!dates.Contains(let.Date))
        {
            dates[counter] = let.Date;
            counter++;
        }
    }
}

Answer 1

You need to change the prototype of the method, but you can do something like:

public static IReadOnlyList<DateTime> FindDates(IEnumerable<Letter> L)
{
    return L.Select(l => l.Date).Distinct().ToList();
}

The value of counter can be retrieved easily by reading the Count property of the result list.

Overall, it's a good practice to avoid side-effects in methods as much as possible. Modifying an array passed as a parameter like you do is a good way to get bitten later.

Also, since the Linq extension methods are defined on IEnumerable<T> , we can change the parameter of the method to IEnumerable<Letter> . It'll work exactly the same with your LinkedList<Letter> , with the added benefit that it won't break if later you decide to use another collection type (such as List<Letter> )