Subject: Re: [boost] bug in boost::variant?
From: Larry Evans (cppljevans_at_[hidden])
Date: 2009-12-11 13:30:34
On 12/10/09 22:11, Zachary Turner wrote:
> I'm using boost 1.41. I use a variant to store a symbolic representation of
> an algebraic expression, wrapped inside of a master "node" class. Like
> this:
>
> struct expr_node
> {
> friend class constant;
> friend class variable;
> friend class arithmetic_op;
> friend class exponent;
> friend class special_func;
> friend class negative;
> public:
> template<class T>
> expr_node(const T& expr)
> : expr_(expr)
> {
> }
>
> expr_node& operator=(const expr_node& rhs)
> {
> expr_ = rhs;
> return *this;
> }
>
> private:
> typedef boost::variant<constant, variable, arithmetic_op, exponent,
> special_func, negative> node_type;
I think some of these variant args should have recursive_wrapper
wrapping them. See the link in following Dec 3 post to this list:
http://sourceforge.net/mailarchive/message.php?msg_name=loom.20091203T005648-860%40post.gmane.org
However, in that code, I don't think there needs to be a
recursive_wrapper<Node>
in the variant's components.
>
> node_type expr_;
> };
>
> Of course, this is a recursive definition, because exponent, arithmetic_op,
> etc also contain expr_node members.
[snip]
HTH.
-regards,
Larry