Comment by moth-fuzz

Regarding the 'Modular Monoliths' bit, I wholeheartedly agree. I always found it kind of disappointing that while we're told in our OOP classes that using interfaces increases modularity and cohesion and decreases coupling, in reality in most programming languages you're relying on the nominal type of said interface regardless. All libraries have to use a common interface at the source code level, which is obscenely rare. For interfaces to truly live up to what they're describing, they merely ought to be structural (or whatever the equivalent to functions is that structural typing is to data).

Edit, since I remembered Go has this behaviour: I think Go's auto-interfaces I think are easily one of its biggest selling points.