## eval.c

rb_mod_append_features(module, include)
    VALUE module, include;
{
    switch (TYPE(include)) {
      case T_CLASS:
      case T_MODULE:
        break;
      default:
        Check_Type(include, T_CLASS);
        break;
    }
    rb_include_module(include, module);

    return module;
}

## class.c

void
rb_include_module(klass, module)
    VALUE klass, module;
{
    VALUE p, c;
    int changed = 0;

    rb_frozen_class_p(klass);
    if (!OBJ_TAINTED(klass)) {
        rb_secure(4);
    }

    if (TYPE(module) != T_MODULE) {
        Check_Type(module, T_MODULE);
    }

    OBJ_INFECT(klass, module);
    c = klass;
    while (module) {
        int superclass_seen = Qfalse;

        if (RCLASS(klass)->m_tbl == RCLASS(module)->m_tbl)
            rb_raise(rb_eArgError, "cyclic include detected");
        /* ignore if the module included already in superclasses */
        for (p = RCLASS(klass)->super; p; p = RCLASS(p)->super) {
            switch (BUILTIN_TYPE(p)) {
              case T_ICLASS:
                if (RCLASS(p)->m_tbl == RCLASS(module)->m_tbl) {
                    if (!superclass_seen) {
                        c = p;  /* move insertion point */
                    }
                    goto skip;
                }
                break;
              case T_CLASS:
                superclass_seen = Qtrue;
                break;
            }
        }
        c = RCLASS(c)->super = include_class_new(module, RCLASS(c)->super);
        changed = 1;
      skip:
        module = RCLASS(module)->super;
    }
    if (changed) rb_clear_cache();
}


static VALUE
include_class_new(module, super)
    VALUE module, super;
{
    NEWOBJ(klass, struct RClass);
    OBJSETUP(klass, rb_cClass, T_ICLASS);

    if (BUILTIN_TYPE(module) == T_ICLASS) {
        module = RBASIC(module)->klass;
    }
    if (!RCLASS(module)->iv_tbl) {
        RCLASS(module)->iv_tbl = st_init_numtable();
    }
    klass->iv_tbl = RCLASS(module)->iv_tbl;
    klass->m_tbl = RCLASS(module)->m_tbl;
    klass->super = super;
    if (TYPE(module) == T_ICLASS) {
        RBASIC(klass)->klass = RBASIC(module)->klass;
    }
    else {
        RBASIC(klass)->klass = module;
    }
    OBJ_INFECT(klass, module);
    OBJ_INFECT(klass, super);

    return (VALUE)klass;
}