Object#remove_instance_variable

VALUE
rb_obj_remove_instance_variable(VALUE obj, VALUE name)
{
    VALUE val = Qundef;
    const ID id = id_for_var(obj, name, an, instance);

    // Frozen check comes here because it's expected that we raise a
    // NameError (from the id_for_var check) before we raise a FrozenError
    rb_check_frozen(obj);

    if (!id) {
        goto not_defined;
    }

    rb_shape_t * shape = rb_shape_get_shape(obj);

    switch (BUILTIN_TYPE(obj)) {
      case T_CLASS:
      case T_MODULE:
        IVAR_ACCESSOR_SHOULD_BE_MAIN_RACTOR(id);
        rb_shape_transition_shape_remove_ivar(obj, id, shape, &val);
        break;
      case T_OBJECT: {
        if (rb_shape_obj_too_complex(obj)) {
            if (rb_id_table_lookup(ROBJECT_IV_HASH(obj), id, &val)) {
                rb_id_table_delete(ROBJECT_IV_HASH(obj), id);
            }
        }
        else {
            rb_shape_transition_shape_remove_ivar(obj, id, shape, &val);
        }
        break;
      }
      default: {
        rb_shape_transition_shape_remove_ivar(obj, id, shape, &val);
        break;
      }
    }

    if (val != Qundef) {
        return val;
    }

  not_defined:
    rb_name_err_raise("instance variable %1$s not defined",
                      obj, name);
    UNREACHABLE_RETURN(Qnil);
}