How do I return an empty collection or default value in C#-CodePudding

so I have a generic function that calls a web service and converts it to whatever type you call the function with. However if you call CallUrl<SomeValue[]> - I don't want to return null, I want to return an empty list. I'm currently returning DefaultOrEmpty() - where that looks like:

private static T DefaultOrEmpty<T>()
{
   return typeof(T).IsArray 
      ? (T)(object)Array.CreateInstance(typeof(T).GetElementType()!, 0) 
      : default;
}

which works, but seems ridiculously complicated - is there a cleaner way to write this function?

CodePudding user response：

Assuming by "collection", you mean an array, specifically, I don't see anything particularly wrong with your array initialization as it's perfectly understandable, but here's a slightly shorter method if that's what you're aiming for:

private static T DefaultOrEmpty<T>()
{
    return typeof(T).IsArray
       ? (T)Activator.CreateInstance(typeof(T), 0)
       : default;
}

Or to support multidimensional arrays (which were not supported in the original method):

private static T DefaultOrEmpty<T>()
{
    if (typeof(T).IsArray)
    {
        var args = Enumerable.Repeat(0, typeof(T).GetArrayRank())
            .Cast<object>()
            .ToArray();
        return (T)Activator.CreateInstance(typeof(T), args);
    }
    
    return default;
}

CodePudding user response：

This is simple enough to just inline.

T[] DefaultOrEmpty<T>()
=> Array.Empty<T>();

Your current code seems to be expecting an array type parameter and then returning an array, and otherwise returning a simple value. That looks weird.

When you pass a TReference[] you will get back a TReference[]

When you pass a TReference you will get back a null rather than empty array.

When you pass a TValue[] you will get back a TValue[].

When you pass a TValue you will get back a TValue (like 0) rather than null or empty.

That may be your intent, it's just quite unusual to pass an array type generic parameter.