Even aside from DRY, extracting a block of code to a function or method gives you an opportunity to name the block of code, which often significantly clarifies the intent of the code so, I’ve always tried to error on the side of overly DRY
When I first took over maintaining Red Moon, I was a very new dev and went a little DRY crazy. In particular, there's a state machine for the different filter states (running, paused, stopped, etc), that had a bunch of classes (one per state) that had a lot of overlap. I pulled some common behaviors out into a supertype that the classes with those behaviors now inherited from.
Except, it turns out some of those states ought to act differently (automatic pauses in secure apps should disable the overlay but not restore the backlight; manual pauses should do both), and now it's going to be extra work untangling the various states and pause logic. If I'd left the state machine (amongst other bits) as it was, this feature/bugfix would be implemented already. Also, the current state of things (pun intended) is a bit less readable, in my opinion.
For instance, one piece of code is supposed to do the same thing as another, but in context it caused a side effect that some other part of the code was inadvertently relying on.
Embarrassing to admit, but until now I didn't think in this perspective - and on hindsight it should be obvious, sometimes code might look duplicate, but is not
Here's the file I was referencing (only 100 lines!): https://github.com/LibreShift/red-moon/blob/master/app/src/m...
Here's the issue I've been putting off fixing because of it: https://github.com/LibreShift/red-moon/issues/208
The problem is that right now there is one PAUSE state, which is triggered by both manual pauses (brightness should be restored) and automatic pauses (in secure apps; brightness should not be restored). The problem wasn't exactly DRY, it's the misapplication: I merged bits that had identical code, but turned out not to have identical purpose.
And, for posterity, here's what it used to look like way back (DRYing was not the only change, I also split out notification stuff, so it's not a 1:1 length comparison): https://github.com/LibreShift/red-moon/blob/11ae916955ff8c36...
edit: and here's the original file, back mostly before I touched it at all: https://github.com/LibreShift/red-moon/blob/ed2ec4fd1c68611d...
Nobody here is saying DRY is bad, just that it's not universally the right thing to do without consideration.
Sometimes it's better to have just a few separate, differently shaped pegs, than one flexible peg that fits any hole but is so complex that it might introduce 10 new bugs along the way.
In many cases, the opportunity for DRY was misleading as the code was only superficially similar, so the implementation became over-complicated to handle various corner cases that otherwise wouldn’t have existed.
