Understanding - or looking up - library functions is something you're always going to have to do during code review (it's well worth getting IDE integration set up). zip is a very standard and well-known function (I used it yesterday, in a non-Rust codebase); it may well end up being better-known than "if let". Learning what a library function does is certainly never harder than learning what a keyword does and it's often easier (apart from anything else, you know that a library function follows the normal rules for functions, so if you can see how its output is used then you can often tell what it does. Whereas you can't rely on that kind of reasoning with language keywords).