Getter

Constructor for Getter — read-only single-focus optic, backed by Direct with T = B = Unit. .get(s) is the only meaningful operation; the write path is vestigial.

Both the leftover T and the back-focus B are Unit, which makes the read-only-ness explicit in the type (there is no B to put back). Getter.apply returns a concrete Getter, so a Getter composes with another Getter through the ordinary andThen (the fused Getter.andThen) — g1.andThen(g2) reads s => g2.get(g1.get(s)) — exactly as Iso / Lens compose via their own fused subclasses.