One year after switching from Java to Go

Man. This works. The context API allows/enables it. But I’d really recommend against passing data to functions via context. The biggest selling point of Go to me is that I can usually just look at anyone’s code and know what it’s doing, but this breaks down when data is hidden inside a context. Dependency injection is entirely possible without using the context package at all, interfaces are great for it.

Just use the dependent package directly. Initialize the package once using init() or Init(). Rely on the built-in package dependency resolver system in Go, which will catch cyclic dependencies, call init() in topo order, and other such things.

Test using monkey-patching. Stop using interfaces just to be able to swap a real thing with a mock implementation. These are all symptoms of writing Java in Go.

TIL Go has monkey-patching.

But since it has monkey-patching, how is it statically typed? Or does Go monkey-patching amount to creating an instance of a defined-on-the-fly subclass?

The latter would be interesting, because Java lets you do this too -- conveniently "new up" an instance of a subclass that you define inline of a given class or interface (this used to be the easiest way to define callbacks, before lambdas came along), so this testing strategy is available to Java too, but seems not to be preferred.

Separate question: IIUC, monkey-patching is convenient if your test code directly needs to create a TestX instead of a real X, but what if you need the test double "deeper down" -- that is, you need an X that creates a Y that creates a TestZ instead of a real Z?