Change format_descriptor::value to a static func

docs/advanced.rst

@@ -1224,12 +1224,12 @@ completely avoid copy operations with Python expressions like
     py::class_<Matrix>(m, "Matrix")
        .def_buffer([](Matrix &m) -> py::buffer_info {
             return py::buffer_info(
-                m.data(),                            /* Pointer to buffer */
-                sizeof(float),                       /* Size of one scalar */
-                py::format_descriptor<float>::value, /* Python struct-style format descriptor */
-                2,                                   /* Number of dimensions */
-                { m.rows(), m.cols() },              /* Buffer dimensions */
-                { sizeof(float) * m.rows(),          /* Strides (in bytes) for each index */
+                m.data(),                              /* Pointer to buffer */
+                sizeof(float),                         /* Size of one scalar */
+                py::format_descriptor<float>::value(), /* Python struct-style format descriptor */
+                2,                                     /* Number of dimensions */
+                { m.rows(), m.cols() },                /* Buffer dimensions */
+                { sizeof(float) * m.rows(),            /* Strides (in bytes) for each index */
                   sizeof(float) }
             );
         });
@@ -1273,7 +1273,7 @@ buffer objects (e.g. a NumPy matrix).
             py::buffer_info info = b.request();
 
             /* Some sanity checks ... */
-            if (info.format != py::format_descriptor<Scalar>::value)
+            if (info.format != py::format_descriptor<Scalar>::value())
                 throw std::runtime_error("Incompatible format: expected a double array!");
 
             if (info.ndim != 2)
@@ -1299,7 +1299,7 @@ as follows:
             m.data(),                /* Pointer to buffer */
             sizeof(Scalar),          /* Size of one scalar */
             /* Python struct-style format descriptor */
-            py::format_descriptor<Scalar>::value,
+            py::format_descriptor<Scalar>::value(),
             /* Number of dimensions */
             2,
             /* Buffer dimensions */

example/example-buffers.cpp

@@ -81,7 +81,7 @@ void init_ex_buffers(py::module &m) {
         /// Construct from a buffer
         .def("__init__", [](Matrix &v, py::buffer b) {
             py::buffer_info info = b.request();
-            if (info.format != py::format_descriptor<float>::value || info.ndim != 2)
+            if (info.format != py::format_descriptor<float>::value() || info.ndim != 2)
                 throw std::runtime_error("Incompatible buffer format!");
             new (&v) Matrix(info.shape[0], info.shape[1]);
             memcpy(v.data(), info.ptr, sizeof(float) * v.rows() * v.cols());
@@ -104,12 +104,12 @@ void init_ex_buffers(py::module &m) {
        /// Provide buffer access
        .def_buffer([](Matrix &m) -> py::buffer_info {
             return py::buffer_info(
-                m.data(),                            /* Pointer to buffer */
-                sizeof(float),                       /* Size of one scalar */
-                py::format_descriptor<float>::value, /* Python struct-style format descriptor */
-                2,                                   /* Number of dimensions */
-                { m.rows(), m.cols() },              /* Buffer dimensions */
-                { sizeof(float) * m.rows(),          /* Strides (in bytes) for each index */
+                m.data(),                              /* Pointer to buffer */
+                sizeof(float),                         /* Size of one scalar */
+                py::format_descriptor<float>::value(), /* Python struct-style format descriptor */
+                2,                                     /* Number of dimensions */
+                { m.rows(), m.cols() },                /* Buffer dimensions */
+                { sizeof(float) * m.rows(),            /* Strides (in bytes) for each index */
                   sizeof(float) }
             );
         })

include/pybind11/common.h

@@ -204,7 +204,7 @@ struct buffer_info {
     void *ptr;                   // Pointer to the underlying storage
     size_t itemsize;             // Size of individual items in bytes
     size_t size;                 // Total number of entries
-    std::string format;          // For homogeneous buffers, this should be set to format_descriptor<T>::value
+    std::string format;          // For homogeneous buffers, this should be set to format_descriptor<T>::value()
     size_t ndim;                 // Number of dimensions
     std::vector<size_t> shape;   // Shape of the tensor (1 entry per dimension)
     std::vector<size_t> strides; // Number of entries between adjacent entries (for each per dimension)
@@ -348,14 +348,22 @@ PYBIND11_RUNTIME_EXCEPTION(reference_cast_error) /// Used internally
 [[noreturn]] PYBIND11_NOINLINE inline void pybind11_fail(const std::string &reason) { throw std::runtime_error(reason); }
 
 /// Format strings for basic number types
-#define PYBIND11_DECL_FMT(t, v) template<> struct format_descriptor<t> { static constexpr const char *value = v; }
+#define PYBIND11_DECL_FMT(t, v) template<> struct format_descriptor<t> \
+    { static constexpr const char* value() { return v; } };
+
 template <typename T, typename SFINAE = void> struct format_descriptor { };
+
 template <typename T> struct format_descriptor<T, typename std::enable_if<std::is_integral<T>::value>::type> {
-    static constexpr const char value[2] =
+    static constexpr const char* value() { return format; }
+    static constexpr const char format[2] =
         { "bBhHiIqQ"[detail::log2(sizeof(T))*2 + (std::is_unsigned<T>::value ? 1 : 0)], '\0' };
 };
+
 template <typename T> constexpr const char format_descriptor<
-    T, typename std::enable_if<std::is_integral<T>::value>::type>::value[2];
-PYBIND11_DECL_FMT(float, "f"); PYBIND11_DECL_FMT(double, "d"); PYBIND11_DECL_FMT(bool, "?");
+    T, typename std::enable_if<std::is_integral<T>::value>::type>::format[2];
+
+PYBIND11_DECL_FMT(float, "f");
+PYBIND11_DECL_FMT(double, "d");
+PYBIND11_DECL_FMT(bool, "?");
 
 NAMESPACE_END(pybind11)

include/pybind11/eigen.h

@@ -133,7 +133,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_dense<Type>::value &&
                 /* Size of one scalar */
                 sizeof(Scalar),
                 /* Python struct-style format descriptor */
-                format_descriptor<Scalar>::value,
+                format_descriptor<Scalar>::value(),
                 /* Number of dimensions */
                 1,
                 /* Buffer dimensions */
@@ -148,7 +148,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_dense<Type>::value &&
                 /* Size of one scalar */
                 sizeof(Scalar),
                 /* Python struct-style format descriptor */
-                format_descriptor<Scalar>::value,
+                format_descriptor<Scalar>::value(),
                 /* Number of dimensions */
                 isVector ? 1 : 2,
                 /* Buffer dimensions */
@@ -233,7 +233,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_sparse<Type>::value>::
             try {
                 obj = matrix_type(obj);
             } catch (const error_already_set &) {
-                PyErr_Clear(); 
+                PyErr_Clear();
                 return false;
             }
         }
@@ -276,7 +276,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_sparse<Type>::value>::
             // Size of one scalar
             sizeof(Scalar),
             // Python struct-style format descriptor
-            format_descriptor<Scalar>::value,
+            format_descriptor<Scalar>::value(),
             // Number of dimensions
             1,
             // Buffer dimensions
@@ -291,7 +291,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_sparse<Type>::value>::
             // Size of one scalar
             sizeof(StorageIndex),
             // Python struct-style format descriptor
-            format_descriptor<StorageIndex>::value,
+            format_descriptor<StorageIndex>::value(),
             // Number of dimensions
             1,
             // Buffer dimensions
@@ -306,7 +306,7 @@ struct type_caster<Type, typename std::enable_if<is_eigen_sparse<Type>::value>::
             // Size of one scalar
             sizeof(StorageIndex),
             // Python struct-style format descriptor
-            format_descriptor<StorageIndex>::value,
+            format_descriptor<StorageIndex>::value(),
             // Number of dimensions
             1,
             // Buffer dimensions

include/pybind11/numpy.h

@@ -351,7 +351,7 @@ struct vectorize_helper {
             return cast(f(*((Args *) buffers[Index].ptr)...));
 
         array result(buffer_info(nullptr, sizeof(Return),
-            format_descriptor<Return>::value,
+                     format_descriptor<Return>::value(),
             ndim, shape, strides));
 
         buffer_info buf = result.request();