The world runs on legacy code. For every greenfield progressive web app with 100% test coverage, there are literally hundreds of archaic line-of-business applications running in production - systems with no tests, no documentation, built using out-of-date tools, languages and platforms. It’s the code developers love to hate: it’s not exciting, it’s not shiny, and it won’t look good on your CV - but the world runs on legacy code, and, as developers, if we’re going to work on anything that actually matters, we’re going to end up dealing with legacy. To work effectively with this kind of system, we need to answer some fundamental questions: why was it built this way in the first place? What's happened over the years it's been running in production? And, most importantly, how can we develop our understanding of legacy codebases to the point where we're confident that we can add features, fix bugs and improve performance without making things worse?

1. Ctrl-Alt-Delete
Learning to Love Legacy Code
t WITH PASSION TO TECHNOLOGY
.NET CONFERENCE #1 IN UKRAINE, KYIV 2018
Dylan Beattie
@dylanbeattie

3. Ctrl-Alt-Delete
Learning to Love Legacy Code
t WITH PASSION TO TECHNOLOGY
.NET CONFERENCE #1 IN UKRAINE, KYIV 2018
Dylan Beattie
@dylanbeattie

4. @dylanbeattie
• Building websites since 1992
• CTO @SkillsMatter
• London .NET User Group
• www.dylanbeattie.net
• dylan@dylanbeattie.net

8. https://www.reddit.com/r/ProgrammerHumor/comments/58lzgc/legacy_code/

11. https://github.com/dotnet/BenchmarkDotNet/src/BenchmarkDotNet/Extensions/ReflectionExtensions.cs

13. "Legacy code is simply
code without tests"
- Michael Feathers

14. Legacy Code:
"Code that's too scary
to update and too
profitable to delete"
https://twitter.com/jbrains/status/998951712546279424

19. http://oldschoolfrp.tumblr.com/image/101938448668

20. Serverless F#
microservices
ASP.NET with
'some tests'
Visual Basic 6
on Windows XP
Excel
Spreadsheets

22. RESUMÉ
• Angular (3 months)
• Blazor (6 months)
• WebAssembly (3 days)
• Rust (4 weeks)
• Kotlin (2 weeks)
• Elm (10 minutes)
RESUMÉ
• C# (15 years)
• SQL Server (25 years)
• HTML (20 years)

24. TRUST CONTROL
UNDERSTANDING

28. Hamlet Moby Dick The Brothers
Karamazov
The Lord of the Rings Atlas Shrugged War and Peace Linux Kernel Mono
Lines
Lines

29. Hamlet Moby Dick The Brothers
Karamazov
The Lord of the Rings Atlas Shrugged War and Peace Linux Kernel Mono
Lines
Lines

32. Observation
Hypothesis
Prediction
Experiment
Analysis
Communication

35. # /etc/hosts
127.0.0.1 api.payments.mycompany.com
127.0.0.1 mail.mycompany.com
127.0.0.1 stockcontrol.mycompany.com

41. IT HAS BEEN
DAYS
SINCE OUR LAST
LEGACY CODE
INCIDENT
29

42. OUR DEFINITION OF "DONE"
qCode deleted
qGitHub repos archived
qDatabases offlined
qServers decommissioned
qTeam at the beach
qDrinking beer

46. Ctrl-Alt-Delete
Learning to Love Legacy Code
t WITH PASSION TO TECHNOLOGY
.NET CONFERENCE #1 IN UKRAINE, KYIV 2018
Dylan Beattie
@dylanbeattie