I really enjoyed the last video, so predictably my reaction is the same this time around.

This one will be a part series as well, strap in for the ride!

What do I think LINQ is?

In the same vein as Async/Await, LINQ is something that I've used a lot but couldn't really conceive of how it works.

Ostensibly it's just a list of helper functions. Things like First Select or Where I'd imagine take a delegate and apply it to a list. Simple, no? I'm anticipating that I might find out that it's a bit more complicated than that.

5 things that I learned while watching this video

• It's still so interesting how iterators work...

That this is a valid function still kind of blows my mind... Luckily we get an explanation.

foreach (int i in GetNumbers())
{
    Console.WriteLine(i);
}
static IEnumerable<int> GetNumbers()
{
    yield return 1;
    yield return 2;
    yield return 3;
}

After compilation, we get something similar to

IEnumerable<int> e = GetNumbers();

using IEnumerator<int> enumerator = e.GetEnumerator();
try {
    while (enumerator.MoveNext())
    {
        int i = enumerator.Current;
        Console.WriteLine(i);
    }
}
finally {
    enumerator?.Dispose();
}

static IEnumerable<int> GetNumbers()
{
    yield return 1;
    yield return 2;
    yield return 3;
}

• So GetNumbers() can somehow store it's state between calls for MoveNext()

• Select() is one of the most basic APIs we use.

  • It's quite literally a foreach loop that yield returns the result of the delegate passed to it.

• Iterators do not execute until MoveNext() is called.

  • So how do we get exceptions to throw e.g. ArgumentNullException?
  • A static iterator method is implemented within the function that does the foreach loop.

• sealed classes provide a performance benefit. Even though Microsoft doesn't recommend using sealed.

  • They also have a tool the identifies classes that aren't inherited, and can benefit from that performance increase.

Where I stopped in the video

I got a little bit carried away. Only 25 minutes in and there's already a ton of information here.

So far:

• Stephen has implemented SelectCompiler()
• Stephen has started to implement his own SelectManualEnumerable<TSource, TResult> to show us how it's implemented.