Comment by Nursie

> One of the interesting patterns happening in Rust is io-less libraries.

Not to join in too much on the "but we already had this!" bandwagon ... but actually to join in the bandwagon - we had these sorts of patterns in C 20 years ago. I worked with a TLS implementation like this sometime around 2005.

Either you work with buffer-in/buffer-out types of scenario, or you register callbacks to do the real IO.

It's a great pattern and means that you can do stuff like change transport mechanism, or put in proxying, or whatever you want really, without having to change the library.

With embedded C stuff it was also relatively common to handle memory allocation this way - buy in a library that does whatever proprietrary thing you need from a vendor, then register your custom allocator with it so when it needed heap memory, you could provide that in line with whatever platform restrictions you had going.