From: eric_at_[hidden]
Date: 2008-05-27 16:01:47
Author: eric_niebler
Date: 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
New Revision: 45831
URL: http://svn.boost.org/trac/boost/changeset/45831
Log:
add proto::protect<> to prevent a nested transform from being applied
Text files modified:
branches/proto/v4/boost/proto/detail/decltype.hpp | 2
branches/proto/v4/boost/proto/fusion.hpp | 2
branches/proto/v4/boost/proto/make_expr.hpp | 2
branches/proto/v4/boost/proto/proto_fwd.hpp | 3 ++
branches/proto/v4/boost/proto/transform/default.hpp | 4 +-
branches/proto/v4/boost/proto/transform/make.hpp | 56 ++++++++++++++++++++++++++++++++++++++++
6 files changed, 64 insertions(+), 5 deletions(-)
Modified: branches/proto/v4/boost/proto/detail/decltype.hpp
==============================================================================
--- branches/proto/v4/boost/proto/detail/decltype.hpp (original)
+++ branches/proto/v4/boost/proto/detail/decltype.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -225,7 +225,7 @@
private:
T obj;
- PMF pmf;
+ PMF pmf;
};
} // namespace detail
Modified: branches/proto/v4/boost/proto/fusion.hpp
==============================================================================
--- branches/proto/v4/boost/proto/fusion.hpp (original)
+++ branches/proto/v4/boost/proto/fusion.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -117,7 +117,7 @@
}
};
}
-
+
namespace result_of
{
template<typename Expr>
Modified: branches/proto/v4/boost/proto/make_expr.hpp
==============================================================================
--- branches/proto/v4/boost/proto/make_expr.hpp (original)
+++ branches/proto/v4/boost/proto/make_expr.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -1013,7 +1013,7 @@
#ifdef _MSC_VER
# pragma warning(pop)
#endif
-
+
#undef BOOST_PROTO_AT
#undef BOOST_PROTO_AT_TYPE
#undef BOOST_PROTO_AS_CHILD_AT
Modified: branches/proto/v4/boost/proto/proto_fwd.hpp
==============================================================================
--- branches/proto/v4/boost/proto/proto_fwd.hpp (original)
+++ branches/proto/v4/boost/proto/proto_fwd.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -729,6 +729,9 @@
template<typename Fun>
struct make;
+ template<typename PrimitiveTransform>
+ struct protect;
+
template<typename Fun>
struct lazy;
Modified: branches/proto/v4/boost/proto/transform/default.hpp
==============================================================================
--- branches/proto/v4/boost/proto/transform/default.hpp (original)
+++ branches/proto/v4/boost/proto/transform/default.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -135,7 +135,7 @@
#undef BOOST_PROTO_UNARY_OP_RESULT
#undef BOOST_PROTO_BINARY_OP_RESULT
-
+
/// INTERNAL ONLY
template<typename Expr, typename State, typename Data>
struct is_member_function_invocation
@@ -330,7 +330,7 @@
, t1(proto::child_c<1>(expr), state, data);
}
};
-
+
#define EVAL_TYPE(Z, N, DATA) \
typedef \
typename result_of::child_c<DATA, N>::type \
Modified: branches/proto/v4/boost/proto/transform/make.hpp
==============================================================================
--- branches/proto/v4/boost/proto/transform/make.hpp (original)
+++ branches/proto/v4/boost/proto/transform/make.hpp 2008-05-27 16:01:46 EDT (Tue, 27 May 2008)
@@ -152,6 +152,56 @@
#undef TMP
}
+ /// \brief A PrimitiveTransform which prevents another PrimitiveTransform
+ /// from being applied in an \c ObjectTransform.
+ ///
+ /// When building higher order transforms with <tt>make\<\></tt> or
+ /// <tt>lazy\<\></tt>, you sometimes would like to build types that
+ /// are parameterized with Proto transforms. In such lambda-style
+ /// transforms, Proto will unhelpfully find all nested transforms
+ /// and apply them, even if you don't want them to be applied. Consider
+ /// the following transform, which will replace the \c _ in
+ /// <tt>Bar<_>()</tt> with <tt>proto::terminal\<int\>::type</tt>:
+ ///
+ /// \code
+ /// template<typename T>
+ /// struct Bar
+ /// {};
+ ///
+ /// struct Foo
+ /// : proto::when<_, Bar<_>() >
+ /// {};
+ ///
+ /// proto::terminal<int>::type i = {0};
+ ///
+ /// int main()
+ /// {
+ /// Foo()(i);
+ /// std::cout << typeid(Foo()(i)).name() << std::endl;
+ /// }
+ /// \endcode
+ ///
+ /// If you actually wanted to default-construct an object of type
+ /// <tt>Bar\<_\></tt>, you would have to protect the \c _ to prevent
+ /// it from being applied. You can use <tt>proto::protect\<\></tt>
+ /// as follows:
+ ///
+ /// \code
+ /// // OK: replace anything with Bar<_>()
+ /// struct Foo
+ /// : proto::when<_, Bar<_>() >
+ /// {};
+ /// \endcode
+ template<typename PrimitiveTransform>
+ struct protect : transform<protect<PrimitiveTransform> >
+ {
+ template<typename, typename, typename>
+ struct impl
+ {
+ typedef PrimitiveTransform result_type;
+ };
+ };
+
/// \brief A PrimitiveTransform which computes a type by evaluating any
/// nested transforms and then constructs an object of that type.
///
@@ -212,6 +262,12 @@
: mpl::true_
{};
+ /// INTERNAL ONLY
+ ///
+ template<typename PrimitiveTransform>
+ struct is_callable<protect<PrimitiveTransform> >
+ : mpl::true_
+ {};
}}
#endif