Free public beta until December 4, 2026: every course is open, no card needed. After that, the first chapter of each course stays free and full access is a one-time $39 ($19 for up to 100 founding members chosen for helpful feedback). Your progress is kept. How the beta works

target type

The functional interface type a lambda or method reference is assigned or passed to.

The type expected by the context of a lambda or method reference; var gives none, so var f = x -> x does not compile.