[Rendello]

> Bump allocator

You can build an ad-hoc bump allocator by using a String and indexing into it. You can't use &str references though, as a growing String may reallocate elsewhere and invalidate your references (Rust won't even let you try this), so you have to use your own indices. This is the same thing that bump allocator libraries usually do, too. It can be tricky but have great performance gains.

I recently 100x-d the speed of an XML/HTML builder I use internally by rewriting it to only have one thing on the heap, a single String. Every push happens right at the call site linearly, and by passing data through closures the formatting (indentation, etc.) is controllable. My first iteration was written in the least efficient way possible and had thousands of tiny allocations in nested heap objects, it was painfully slow.