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Use Of Rust To Construct A Suite Of Small Algorithm Design and Validation Executables and Supporting Infrastructure

Bart Massey Rust for Advent Of Code 2016

Bart Massey

Advent Of Code 2016

  • Eric Wastl, http://adventofcode.com/2016 (also 2015)

  • Series of 25 small programming challenge problems

  • "Advent Calendar" format

  • Roughly increasing difficulty

  • Usual single-answer

  • Great sense of humor, statistics, competition

My History: Advent of Code 2015 In Haskell

Advent of Code 2016 In Rust

Let's Do Day 1!

  • Part 1 is really straightforward

  • Note that there's a lot of fairly ugly boilerplate

    • Reading a line from a file

    • String manipulation and number parsing

Day 1 Part 2

  • Need to detect self-intersection of path

  • Rust HashSet is perfect for this

  • Note that memory management really isn't an issue here

The Rest Of The Days

  • Kinds of problems: straight puzzles, simulations, brute-force calculations

  • Difficulty from a few minutes to "I don't think I can do this"

  • The theming is nice and keeps it interesting

  • Nice endgame (on Christmas Day!)

Programs + Infrastructure = Solution

  • Bunch of related problems means common code

    • Maps and directions, A* search, RTL assembler

  • Standard programming-puzzle means common code

    • Argument processing, primes and factoring, integer square root, popcount, combinatorics

  • Rust limitations mean common code

    • Hexadecimal numbers, iterator over lines of a file

Assembunny

  • Several of the problems require parsing and executing assembly code for a hypothetical machine

  • Extracting the assembler is a big clarity win

  • Also allows performance improvements: 318 MAIPS

Special Setup and Build

  • Not written in Rust but in Bourne Shell

    • mkday.sh: Set up a new day's subdirectory
    • process-aoc.sh: Mangle copy-paste of problem into archival format (using Pandoc)

  • Makes each day's setup fast because muh leaderboard

  • Hopefully reusable for 2017

The Organization Is Partly A Lie

  • I've presented the organization of this stuff as though I chose it in advance

  • In truth, it all grew fairly organically

  • In particular, a lot of stuff was split out and cleaned up after the contest was over, in prep for publication

Rust Issue: Binaries Are Second-Class Citizens

  • Cargo support for binaries is limited

    • Binaries sharing a library does not work well

    • Cannot install arbitrary dependencies of binary

  • Rustdoc does not binary much

    • No support for things like argument descriptions

    • cargo rustdoc --open -- --no-defaults --passes collapse-docs \ --passes unindent-comments --passes strip-priv-imports

  • Not great support for end-to-end binary tests

Final Thoughts

  • Rust is ready for this kind of task

  • A reasonable person with reasonable Rust knowledge can build quickly and cleanly

  • It would be good to have Rust developers sit with newer users and watch them work through an exercise like this