LINQ in .NET - Things I learned #2

We're back with part 2! You can find part 1 here!

I've got a long train ride, so I'm not sure where I'll stop with this one.

Here's where we left off:

We're trying to re-implement Select() from scratch
Stephen has implemented SelectCompiler()
Stephen has started to implement his own SelectManualEnumerable<TSource, TResult> to show us how it's implemented
Stephen also started to implement his own Enumerator: IEnumerator<TResult> class

Here's the video! Let's get into it.

5... or more things I learned watching this video

object Current in IEnumerator has nullable reference types disabled in the .NET Source. "Oblivious" as the source puts it.
- A great reminder that https://source.dot.net/ exists.
Reset() will throw a NotSupportedException(). Most Enumerators in .NET will do this... pretty interesting.
throw e is not the same as throw
- throw e will change the stacktrace information!!

try {
    ...
}
catch (Exception e) {
    throw e;
}

Bad Example: throw e will change the stacktrace information!

try {
    ...
}
catch {
    throw;
}

Good Example: throw knows how to preserve the stacktrace information on its own.

Enumerators track their state so that they know where to resume from.
- e.g. 1 = initialise enumerator, 2 = perform MoveNext()
Watching Stephen code is interesting. I've never thought about zoom level as a tool to view my progress in implementation.
You can use _ to separate numbers?! 10_000 is the same as 10000. You can bet I'll probably use that for visual clarity.

The end of the train ride is coming up. Let's continue on the way back.

Where we left off:

Timestamp: 1:01:08 (TODO: grab the link once I get internet)
Looking at the profiler, Stephen's implementation creates an extra object.
Stephen refactored out the sealed Enumerator class and let's the SelectManualEnumerable be it's own Enumerator instead.
However, now things are broken, an extra state needs to be accounted for.