Why is List.Enumerator faster than my implementation?

Question

I\'ve found myself in a position where I have to roll my own dynamic array implementation, due to various large performance benefits (in my case). However, after creating an enu

Answer 1

Okay, aside from benchmarking problems, here's how you can make your DynamicArray class more like List:

public DynamicArrayEnumerator GetEnumerator()
{
    return new DynamicArrayEnumerator(this);
}

IEnumerator IEnumerable.GetEnumerator()
{
    return GetEnumerator();
}

IEnumerator IEnumerable.GetEnumerator()
{
    return this.GetEnumerator();
}

Now, code which knows it's working with a dynamic array can iterate with a DynamicArrayEnumerator without any boxing, and without virtual dispatch. This is exactly what List does. The compiler notices when a type implements the pattern in a custom manner, and will use the types involved instead of the interfaces.

With your current code, you're getting no benefit from creating a struct - because you're boxing it in GetEnumerator().

Try the above change and fix the benchmark to work for longer. I'd expect to see a big difference.