[geogriffin]

I'm an erlang fan but I wouldn't claim message passing is "fast" in the sense that you might be thinking of (though copying data does have some GC and CPU cache performance benefits that are harder to reason about.) There's no magic in Erlang; copying data is copying data. The benefits of Erlang lie elsewhere, and I've heard Joe Armstrong, when asked about BEAM performance, say something along the lines of "why do you care about performance [in this day and age]?"

[_asummers]

With OTP20, copying data isn't always necessary anymore :)

[jlouis]

Copying data is usually necessary in OTP 20 as well I'm afraid. That new optimization doesn't trigger for most of this. But binary data is not copied and hasn't been since at least OTP11 :)

[_asummers]

The release says "Erlang literals". Wouldn't that be things like atoms, integers, booleans, tuples, and the like? That plus binary data should cover a good deal, unless I'm reading too much into the blurb on the release notes.

Under what circumstances does it get triggered (since you seem to be more knowledgable about this than I am!)? I expect records would not fall under this.

[jlouis]

A "literal" in this case is a constant value defined in a module. Those live in a separate space in the VM and are referenced directly because they are immutable and can be shared. If you sent such a literal before OTP20, it would be copied into the heap of the target process. Not anymore.

But it doesn't help with cases where you are constructing a term (dynamically) in a process and sending that term. There is more meat in the blog post of mine: https://medium.com/@jlouis666/an-erlang-otp-20-0-optimizatio...