Function mrb_class_get_under 

pub unsafe extern "C" fn mrb_class_get_under(
    mrb: *mut mrb_state,
    outer: *mut RClass,
    name: *const c_char,
) -> *mut RClass

Gets a child class. @param mrb The current mruby state. @param outer The name of the parent class. @param name The name of the class. @return [struct RClass *] A reference to the class.