dup

static VALUE
binding_dup(VALUE self)
{
    VALUE bindval = rb_binding_alloc(rb_cBinding);
    rb_binding_t *src, *dst;
    GetBindingPtr(self, src);
    GetBindingPtr(bindval, dst);
    dst->env = src->env;
    dst->path = src->path;
    dst->blockprocval = src->blockprocval;
    dst->first_lineno = src->first_lineno;
    return bindval;
}