01
Will It Build?
43 minThis might sound crazy, but all I want is to get this thing to build. We take our time inside the SubSonic codebase and come out the other side with a concept of a plan, which is not quite the same as a plan.
2006
First commit
3.5→10
.NET, in public
3
Episodes · 2h 36m
20yr
Of my own decisions
01Person
Every shop has a codebase
nobody wants to touch.
It works, mostly. It makes money, definitely. And every year the gap between what it runs on and what you would hire for gets a little wider. Nobody gets promoted for touching it, and everyone is quietly dreading the day they have to.
Mine is called SubSonic. I wrote it, it shipped inside real products, and it has been sitting on .NET 3.5 since roughly the year the iPhone came out. So rather than upgrade it quietly, I asked Jon Skeet to do it with me in front of a camera.
“Owning every questionable decision in the codebase, and explaining them under oath.”
"
SubSonic is the patient. The procedure is the point, and it transfers to whatever twenty-year-old codebase is haunting your shop.
What this series is
Read before you buy
02Problem
The migration guides
assume a clean repo.
They want a tidy solution file, passing tests, and a team with spare time. Your legacy code has none of those things, which is exactly why the guides do not help and why the upgrade keeps sliding to next quarter.
What helps is watching two people actually do it, out loud, with the dead ends left in. We do not know what will work either. That is the honest part, and it is the part you can copy.
The cost of waiting
Every year you postpone, the jump gets bigger and the people who remember how it works get further away.
03Story
In 2006, I was tired of writing
data access code by hand.
So I wrote SubSonic. It got popular, it shipped inside real products, and then, like all of us, it got older. It is still out there, still full of decisions that made perfect sense at the time and look deranged today.
2006
First commit
Sep 28
2008
Everybody uses it
ASP.NET era
2011
The web moves on
and it stops
2016
Frozen on .NET 3.5
still shipping
2026
The upgrade, live
with Jon Skeet
The sessions are edited hard, so you get the decisions, the arguments, and the dead ends worth seeing, with none of the waiting for builds.
05Solution
A repeatable process
for rescuing old code.
Every session maps to a step you can run on your own codebase the next morning.
01
The Audit
Reading a codebase you did not write, or wrote and forgot, so you can size the job honestly. No more "it is 90% done" for six straight months.
02
The Safety Net
Characterization tests around untested code so you can change it without breaking behavior nobody remembers. You refactor with confidence instead of prayer.
03
The Migration Path
Old csproj to SDK-style, .NET 3.5 to .NET 10, in an order that keeps the build green while the foundation changes underneath it.
04
Modern C# on Old Bones
Jon applying two decades of language evolution: nullable reference types, generics, modern APIs. What to adopt, and what to leave exactly where it is.
05
AI on Legacy Code
Where Claude genuinely helps with a big migration and where it will cheerfully wreck it. The speed without the slop, which is the difference between weeks and quarters.
06
The Ship Decision
Knowing when it is done: what to modernize, what to leave alone, how to release. The project ends instead of becoming the new legacy problem.
·Who's in the room
Two people who have
seen some things.
JS
Jon Skeet
Author, C# in Depth
The top-ranked contributor in Stack Overflow history. If it is in the C# spec, Jon has an opinion about it, and he is usually right. He brings the language depth this upgrade deserves, and the refusal to accept any claim without a repro.
C# in Depth#1 on Stack Overflow, ever
RC
Rob Conery
Creator of SubSonic
Wrote the code we are fixing. Founded Tekpub, wrote The Imposter's Handbook, and spent a decade at Microsoft including three years on the VS Code team. Owns every questionable decision in this codebase.
Creator: SubSonicAuthor: The Imposter's Handbook
06Sell
Why watch someone else’s
upgrade at all?
Because the hard parts of a migration are never the syntax. They are the order you do things in, the moment you decide a rewrite is cheaper than a fix, and the discipline to keep the build green while the ground moves.
You get Jon on the language, me on twenty years of my own bad decisions, and Claude Code in the middle doing the work that used to take a week of evenings. Nothing is rehearsed, which is the only reason it is useful.
What you are buying
3 episodes nowEvery future sessionLifetime accessPublic repo
$79one time · lifetime access · no subscription required