Efficient jagged arrays

A data structure that comes up fairly often when working with graphs or graph-like structure is a jagged array, or array-of-arrays. It’s very simple to build it out of standard containers but that’s often a poor choice for performance; in this post we’ll talk about a simple representation/construction code that I found useful across multiple different projects and domains.

Crucially, we will focus on immutable structures - ones that you can build in one go from source data and then continuously q...