Code inspection: Return type can be IEnumerable<T> (non-private accessibility)

If a method returns a more generic type, it allows for more flexibility. For example, you can change the method's implementation without the need to update usages.

Also, returning a more generic type may help in the future if you decide to change the return value to a more specific type, for example, List<T>: if callers expect IEnumerable<T>, they will be able to accept List<T>, but not vice versa.

Below, ReSharper suggests changing the return type of GetNumbers() from List<String> to IEnumerable<String>:

Note that such a replacement is not always possible, though. If methods of the derived type are used on the returned object anywhere in the solution, ReSharper will not issue this suggestion.

            
class EnumerableTDemo
{
    public static void Main()
    {
        string output = string.Join(" ", GetNumbers());
        Console.WriteLine(output);
    }

    public static List<string> GetNumbers()
    {
        var Numbers = new List<string> {"1", "2", "3"};
        return Numbers;
    }
}

        

            
class EnumerableTDemo
{
    public static void Main()
    {
        string output = string.Join(" ", GetNumbers());
        Console.WriteLine(output);
    }

    public static IEnumerable<string> GetNumbers()
    {
        var Numbers = new List<string> {"1", "2", "3"};
        return Numbers;
    }
}

        

In some cases, however, returning a more specific type might be better. If a method is intended to work only with a specific type like an Array, and its implementation is unlikely to be changed in the future, you can suppress this inspection for that method.

Last modified: 08 April 2024