On 08/06/2011 07:30 AM, Eric Niebler wrote:
On 8/5/2011 8:52 AM, Joel falcou wrote:
There is few use case where I wish i can have a proto::switch_ like
transform being extendable externally but based on something else than
the expression tag like the result of an arbitrary meta-function.
Is cloning proto::swicth_ and changing the way it dispatch over its
internal cases_ enough ?
That wouldn't be enough because proto::matches "knows" about
proto::switch_. It would be easy enough to extend proto::switch_ to take
an optional mpl metafunction that accepts and expression and returns a
type to dispatch on. It would default to proto::tag_of<mpl::_>. Or for
the sake of consistency with the rest of proto, it should probably be a
transform, in which case it would default to proto::tag_of<proto::_>().
Could you open a feature request?
Why not just add an extra class Enable = void template parameter to
case_, which would allow to use SFINAE for case_ partial specializations?
template<class Tag>
struct case_<Tag, typename boost::enable_if< is_what_I_want<Tag> >::type>
: ....
{
};
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