Hi,
I recently discovered a behavior which i find quite odd:
proto::matches<Expression, Grammar>::type fails when Expression is not a
proto expression. I would have expected that it just returns false in
this case. What am I missing. Patch is attached for what i think would
be a better behavior of that meta function.
Regards,
Thomas
Index: boost/proto/matches.hpp
===================================================================
--- boost/proto/matches.hpp (revision 81703)
+++ boost/proto/matches.hpp (working copy)
@@ -500,7 +500,7 @@
/// <tt>[0,n)</tt>, \c Ax and \c Bx are types
/// such that \c Ax lambda-matches \c Bx
template<typename Expr, typename Grammar>
- struct matches
+ struct matches<Expr, Grammar, typename Expr::proto_is_expr_>
: detail::matches_<
typename Expr::proto_derived_expr
, typename Expr::proto_grammar
@@ -511,13 +511,18 @@
/// INTERNAL ONLY
///
template<typename Expr, typename Grammar>
- struct matches<Expr &, Grammar>
+ struct matches<Expr &, Grammar, typename Expr::proto_is_expr_>
: detail::matches_<
typename Expr::proto_derived_expr
, typename Expr::proto_grammar
, typename Grammar::proto_grammar
>
{};
+
+ template<typename Expr, typename Grammar, typename Enable>
+ struct matches
+ : mpl::false_
+ {};
/// \brief A wildcard grammar element that matches any expression,
/// and a transform that returns the current expression unchanged.
Index: boost/proto/proto_fwd.hpp
===================================================================
--- boost/proto/proto_fwd.hpp (revision 81703)
+++ boost/proto/proto_fwd.hpp (working copy)
@@ -521,7 +521,7 @@
template<typename T, typename Void = void>
struct domain_of;
- template<typename Expr, typename Grammar>
+ template<typename Expr, typename Grammar, typename Enable = void>
struct matches;
// Generic expression metafunctions and
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