Expand description
MXL111: s4_* method name on #[miniextendr(s4)] impl.
S4 codegen auto-prepends s4_ to every instance method name when generating
the R generic. A Rust method named s4_foo on an #[miniextendr(s4)] impl
produces an R generic s4_s4_foo, making it unreachable via the expected
s4_foo(obj, ...) call.