I can totally relate to this. Programming in Erlang felt so natural compared to the knots I was twisting myself into writing C++. I was churning out C++ code, but wasn't having fun. Suddenly Erlang made it fun and programming became addictive.
> Suddenly Erlang made it fun and programming became addictive. I'm saying this with complete sincerity: WHAT IS IT THAT YOU PEOPLE SEE!? What is the fun? What are you addicted to? Typing and seeing the output? Solving a problem? I feel like I am missing out on some amazing life altering experience when I see people state that. The same thing I have with the article - what does it mean to love a programming language?
I've fought null pointer exceptions longer than I want to in C# servers and Python code. Usually because we're introspecting into a message that a system sent us, we expect it to have a field on the message, we failed to check for the existance of that field / the field to not be null, and bam null-pointer exception.
Sure, add another guard clause... Every time you run into it. Every time the server crashes and it's a serious problem and someone forgot to set a restart policy on the container... Sometimes you don't know exactly what cascade of messages caused the whole thing to unwind. So tedious. So repetitive.
With GenServers, you've carefully defined that those parts of your system have active, in-memory state, and everything else must be a pure function. Messages come in a FIFO queue to your GenServer.
With pattern-matching, you define exactly what shape of message / fields on the message, and if it doesn't match that, you can either log it, or crash that GenServer.
Which normally would be catastrophic, but since you tied your GenServer to a SupervisionTree with a restart policy (which is trivial to write), if anything happens that you didn't expect, you can Let It Fail. The GenServer crashes and is immediately restarted, with a clean slate, with the correct peer-services in the correct state. Sure, the message that crashed your server was "lost" (there are options to push it to a dead-letter-queue on exit) and you have a bad-state and bad-message to debug in the crash-dump, but your server is still going. It hasn't stopped, it just dropped unexpected messages and has a deterministic recovery pattern to clear all bad-state and start again.
So instead of your message handling code starting with a bunch of defensive sanity checks, with the real meat of the function in the last 5 lines.... you just say "My GenServer is here in this SupervisorTree, I expect an inbound message to look roughly like this, and I will do this with it, done". Suddenly the server will handle the messages it knows how to handle, and everything it cannot handle it will drop on the floor.
Think of this! The server just stays up and keeps going! Anything it cannot handle is not a fatal exception, but a log message. And you didn't have to bend the code into an unnatural shape where you trapped and logged all exceptions and bubbled them up in specific error checks... it's just designed to do it that way out of the box.