Hi,
I have been trying to extend a domain by "subdomaining" it. The sole purpose
of this subdomain was to allow another type of terminal expression.
Please see the attached code, which is a very simplified version of what I
was trying to do.
Ok, so let me try to explain what happens with a small table showing what
works, and what not (fixed size font helps here).
expression | compiles? | matches grammar1? | matches grammar2?|
-------------+-----------+-------------------+------------------+
1. t1 | yes | yes | no |
2. t1 + t1 | yes | yes | no |
3. t2 | yes | no | yes |
4. t2 + t2 | no | no | no |
5. t1 + t2 | no | no | no |
So, 1.-3. are working as expected. 4. and 5. obviously doesn't work
(operator+ gets SFINAE'd out because of these rules:
https://svn.boost.org/trac/boost/ticket/4668
So far so good ... Or not.
Let me remind you that I want to get 4. and 5. compiled, matching grammar2,
but not grammar1.
One attempt would be to change grammar1 to:
struct grammar1
: proto::or_<
proto::plus<proto::_, proto::_>
, int_terminal
>
{};
Which enables the operator+ for 4. however, the expressio 4. starts to match
both grammars. Not really what I.
Expression 5. still fails, and i could not get it to work.
So, How to handle that correctly?
Let me remind you, that adding double_terminal to grammar1 not an option.
Regards,
Thomas
#include <boost/proto/proto.hpp>
namespace proto = boost::proto;
typedef proto::terminal<int> int_terminal;
typedef proto::terminal<double> double_terminal;
template <typename Expr>
struct actor1;
struct grammar1;
struct domain1
: proto::domain<
proto::pod_generator<actor1>
, grammar1
, proto::default_domain
>
{};
struct grammar1
: proto::or_<
proto::plus<grammar1, grammar1>
, int_terminal
>
{};
template <typename Expr>
struct actor1
{
BOOST_PROTO_BASIC_EXTENDS(Expr, actor1<Expr>, domain1)
};
template <typename Expr>
struct actor2;
struct grammar2;
struct domain2
: proto::domain<
proto::pod_generator<actor2>
, grammar2
, domain1
>
{};
struct grammar2
: proto::or_<
grammar1
, double_terminal
>
{};
template <typename Expr>
struct actor2
{
BOOST_PROTO_BASIC_EXTENDS(Expr, actor2<Expr>, domain2)
};
actor1<int_terminal::type> t1 = {{0}};
actor2<double_terminal::type> t2 = {{0}};_______________________________________________
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