One problem with decoupling IO is that you still somehow need to get the data deep down into those places where it's needed by your application logic. That means you end up either:
1. Passing each individual little piece of data separately down the call stack with bloated method signatures containing laundry lists of data that seemingly have nothing to do with some of the contexts where they appear.
2. Combining pieces of data into larger state-holding types which you pass down the call stack, adding complexity to tests which now need mocks.
I think one of the toughest parts of day-to-day software engineering is dealing with this tension when you have complex modules that need to pass a lot of state around. It's easier and cleaner to pull stuff out of global state or thread contexts or IO, but that makes it harder to test. More often than I would like to admit, I ask myself whether a small change really needs an automated test, because those shiny tests that we adore so much sometimes complicate the real application code a lot.
If anyone has thoughts on how they approach this problem (which don't contain the words "dynamic scoping" :P) I'd love to read them.
1. Passing each individual little piece of data separately down the call stack with bloated method signatures containing laundry lists of data that seemingly have nothing to do with some of the contexts where they appear.
2. Combining pieces of data into larger state-holding types which you pass down the call stack, adding complexity to tests which now need mocks.
I think one of the toughest parts of day-to-day software engineering is dealing with this tension when you have complex modules that need to pass a lot of state around. It's easier and cleaner to pull stuff out of global state or thread contexts or IO, but that makes it harder to test. More often than I would like to admit, I ask myself whether a small change really needs an automated test, because those shiny tests that we adore so much sometimes complicate the real application code a lot.
If anyone has thoughts on how they approach this problem (which don't contain the words "dynamic scoping" :P) I'd love to read them.