Deep object cloning/inspection, URL parsing/generator. Date arithmetic. Locking. Caching. Testing. Templating. I've had to rip so many of these out for being fundamentally unworkable and often wrongheaded solutions to already solved problems that it's become a cliche in my career.
I'm not trivializing problems. And I agree people writing wholly new solutions to complicated things is a hilarious cliche. I'd never say, "go write your own JSON parser." And like you said, they're already solved problems. That means there are many ways to DIY, including forking, or cloning just the parts you need.
Deep object cloning/inspection, URL parsing/generator. Date arithmetic. Locking. Caching. Testing. Templating. I've had to rip so many of these out for being fundamentally unworkable and often wrongheaded solutions to already solved problems that it's become a cliche in my career.