The little legacy code that could: a fable of software ownership

Report Generator (RPG) is designed for an 80 column punch card. Put a F in column 6 to mean this, put a "C" to mean something else, match one of the 99 variables (named, intuitively 01 through 99) to make output happen.

I had the distinct displeasure in 1984 of trying to maintain a warehouse stock control system that some evil people had decided to implement in RPG. From memory, RPG only has the equivalent of single dimensioned arrays, so the location of items in the warehouse was an intersection of three arrays pointing to yet another array containing the SKUs.

It's designed to take one or more input files with defined columns in each row (card) and do some stuff (mostly subtotalling etc) and produce output.

Of course, it's been stretched beyond all recognition since it was introduced in 1959. It's literally 60 years old this year.

People have been using source code control since then, but the history of computing is of wheel reinvention and not-invented-here, so we are condemned to rediscover things.

Unit testing is useful for business logic, not for individual functions. If you're writing unit tests around whether or not you go outside an array bound, then you're testing the wrong thing. If, on the other hand, you're making sure that someone under 13 can't signup for a service, that's a reasonable unit test.

DI can be useful for running code, allowing you to instrument the code to identify problems. But that's runtime DI, not compile/deployment time.

As a design pattern, it's more an abstraction / reduction of general parameterized polymorphism, usually dragging in an opinionated framework that requires you to follow a set pattern of development and deployment.

That's your characterization and not all how development works in practice. The vast majority of software barely has anything like versioning and a scant few have maintenance/support windows. That's a fact by volume.

Defining the term "Legacy" to mean something specific as a subjective point of reference (since there is no formal definition), eg

> Legacy until relatively recently meant "Not supported" i.e. Windows XP is "Legacy" whereas Windows 7 is not

is helpful, because it lets me understand what you are thinking, clearly. This does not change my position, as my experience is that working code is still called legacy internally, all the time. The historic resource problems with things like broken dependency chains (you can't even build it anymore), or availability of platforms to test on, is common.