Question

I am trying to determine if a runtime type is some sort of collection type. What I have below works, but it seems strange that I have to name the types that I believe to be collection types in an array like I have done.

In the code below, the reason for the generic logic is because, in my app, I expect all collections to be generic.

bool IsCollectionType(Type type)
{
    if (!type.GetGenericArguments().Any())
        return false;

    Type genericTypeDefinition = type.GetGenericTypeDefinition();
    var collectionTypes = new[] { typeof(IEnumerable<>), typeof(ICollection<>), typeof(IList<>), typeof(List<>) };
    return collectionTypes.Any(x => x.IsAssignableFrom(genericTypeDefinition));
}

How would I refactor this code to be smarter or simpler?

Answer 1

Really all of these types inherit IEnumerable. You can check only for it:

bool IsEnumerableType(Type type)
{
    return (type.GetInterface(nameof(IEnumerable)) != null);
}

or if you really need to check for ICollection:

bool IsCollectionType(Type type)
{
    return (type.GetInterface(nameof(ICollection)) != null);
}

Look at "Syntax" part:

• List<T>

• IList

• ICollection

If you need to exclude strings (which are essentially an IEnumerable<char>), use the following function:

bool IsEnumerableType(Type type)
{
    return (type.Name != nameof(String) 
        && type.GetInterface(nameof(IEnumerable)) != null);
}