Merge branch 'ion-part-2' into 'master'

RSoC: Ion as a Library, week 2

See merge request !211

content/news/rsoc-ion-lib-1.md

+---
+title: "RSoC Project: Ion as a library, week 2"
+author: AdminXVII
+date: 2019-06-16T11:01:32-04:00
+---
+
+# Keyword of the week: Error bubbling
+
+## Summary of the work done
+ - Use enum types to represent error rather than strings
+ - Use the `err_derive` crate to implement easily the required traits for error types
+ - Indicate the cause of errors for easier debugging
+ - Exit the script on the first programmer error (wrong function signature, invalid expansion, assignment error), rather than leaving "magic" happen
+ - Separate parsing & expansion to make it easier to swap the current parser for nom
+ - process::exit is no more used in the library to make execution more linear
+
+## Plan: Testing tendrils
+### Current state & the small string optimization (SSO)
+Ion now uses small::String to store string data types. It's an alternative String type that uses SSO to achieve better performance than the std one with typically small strings.
+
+In Ion's real world usage, strings tend to be fairly short (~ under 20 chars). The small string optimization is a technique where a string is a tagged union containing either a pointer to a heap string (like the one provided by the stdlib) or a stack-based array which is typically faster since it's stored with the containing datastructure that's already in a cache line. According to previous benchmarks, the switch to small strings gave Ion a 30% speed bump.
+
+### The alternative: [tendrils](https://github.com/servo/tendril)
+Tendril is an alternative "compact string/buffer type, optimized for zero-copy parsing". It combines the small string and copy-on-write optimizations, possibly providing another performance boost. Further benchmarks will be needed.
+
+## What's left to do
+ - Finish using error types in expansion
+ - Documentation
+ - Examples
+ - Add background jobs callbacks
+ - Add option to provide custom files for default standard pipes
+ - Release or remove members to be able to publish on crates.io