dup

static VALUE
proc_dup(VALUE self)
{
    VALUE procval;
    rb_proc_t *src;

    GetProcPtr(self, src);
    procval = rb_proc_create(rb_cProc, &src->block,
                             src->safe_level, src->is_from_method, src->is_lambda);
    RB_GC_GUARD(self); /* for: body = proc_dup(body) */
    return procval;
}