keroami / expensereport

The ExpenseReport legacy code refactoring kata in >50 programming languages (Ada to Zig)

ExpenseReport

The ExpenseReport legacy code refactoring kata in various languages.

This is an example of a piece of legacy code with lots of code smells. The goal is to support the following new feature as best as you can:

• Add Lunch with an expense limit of 2000.

Process

1. 📚 Read the code to understand what it does and how it works.
2. 🦨 Read the code and check for design and code smells. Make a list of all code and design smells that you find.
3. 🧑‍🔬 Analyze what you would have to change to implement the new requirement without refactoring the code.
4. 🧪 Write a characterization test. Expand your list of code and design smells. Add those smells that you missed earlier and discovered now because they made your life writing a test miserable.
5. 🔧 Refactor the code.
6. 🔧 Refactor the test.
7. 👼 Test-drive the new feature.

Supported Languages

The ExpenseReport example currently exists in the following languages:

• Ada
• Assembler (Motorola 68020, Amiga OS, MaxonASM)
• Assembler (AArch64, Linux, GNU Assembler)
• Assembler (AMD64/Intel x86-64, Linux, GNU Assembler)
• bash
• BASIC (Amiga BASIC, Commodore Amiga) ⇐ Quite amazing! First BASIC without line numbers!
• BASIC (Bywater BASIC, Linux) (very similar to Commodore BASIC)
• BASIC (Commodore BASIC, Commodore 64)
• BASIC (Locomotive BASIC, Amstrad CPC)
• BASIC (Yabasic)
• C
• C#
• C++
• Clojure ⇐ This one was particularly painful to intentionally write poorly, I almost cried.
• COBOL
• D
• Dart
• Elixir
• F#
• Fortran
• Go
• Groovy
• Haskell
• Java
• JavaScript
• Julia
• Kotlin
• Lisp (Common Lisp)
• Lua
• Nim
• Objective-C
• Pascal
• Perl
• PHP
• PostScript
• Prolog
• Python
• Raku (Perl6)
• Rexx (tested with Regina Rexx and ARexx)
• Ruby
• Rust
• Scala
• Scheme
• Smalltalk
• SQL (Using SQLite3)
• Swift
• TcL
• TypeScript
• Visual BASIC
• XML/XSLT
• Zig
• zsh

Planned languages

(in no particular order and with no guarantee)

• ABAP
• Amiga E
• AMOS BASIC
• APL
• More Assembler implementations (arm, aarch64, i686, powerpc, powerpc64, mpis, mips64, sparc, sparc64, risc-v, etc, usually on Linux)
• Carbon
• CLIPS
• Cluster
• Concurnas
• Curry
• Dark
• Eiffel
• Elm
• Erlang
• Flix
• Forth
• Gleam
• Gosu
• Hack
• Hare
• Java Byte Code / JVM Assembler
• Lobster
• Logo
• Mercury
• Modula-2 (once the linker starts working again)
• Mojo
• Oberon
• OCaml
• Pony
• PureScript
• R
• Reason
• REBOL
• Scratch
• SNOBOL
• Solidity (maybe)
• TeX
• Unison
• WebAssembly

Languages explicitly not planned

• Brainfuck
• False
• Malbolge
• Whitespace

Undecided Languages

There are many more programming languages than in the list above. Find a more complete list on Wikipedia.

Other plans

• Make sure that all languages are providing the identical challenge. To be practical, this will require the removal of the timestamp side-effect.
• Provide the time-stamp side-effect on a separate branch.
• Provide a test setup (without test) on a separate branch so that folks can choose whether they want to include the setup work in the kata or not.
• Provide a level 2 challenge for creating an HTML report besides the Plain Text report.

Solutions

To see solutions, switch to the solutions branch.

Warning The solutions branch will be rebased!

Credits and License

I first encountered the ExpenseReport example during a bootcamp at Equal Experts. I also have seen the ExpenseReport example being used by Robert "Uncle Bob" C. Martin. However, he seems to not be the original author (https://twitter.com/unclebobmartin/status/1537063143326855176?s=20&t=lh_vVb9jUQmY6PYG50974w) I have tried to research its origins but so far I have failed. If you know who has first come up with this example, please get in touch with me.

As I was asked for the license conditions, I have decided to put this under CC-BY-SA, with the following considerations:

• Please credit me, last but not least to retain the opportunity for people to experience this exercise in as many programming languages as they are interested in.
• Share it under the same license.
• Using this as training material should be allowed, even if the trainer is charging money for their time.

Disclaimer: As stated above, I did not come up with the original version. The original author is unknown to me. The CC-BY-SA license thus can only cover my contribution: Recreating the Java version from memory, creating the versions in other programming languages than Java, and keeping them consistent.