Add value_type member alias to py::array_t (resolve pybind#632)

Author: dean0x7d

include/pybind11/numpy.h

@@ -577,6 +577,8 @@ class array : public buffer {
 
 template <typename T, int ExtraFlags = array::forcecast> class array_t : public array {
 public:
+    using value_type = T;
+
     array_t() : array(0, static_cast<const T *>(nullptr)) {}
     array_t(handle h, borrowed_t) : array(h, borrowed) { }
     array_t(handle h, stolen_t) : array(h, stolen) { }

tests/test_numpy_array.cpp

@@ -17,6 +17,7 @@
 
 using arr = py::array;
 using arr_t = py::array_t<uint16_t, 0>;
+static_assert(std::is_same<arr_t::value_type, uint16_t>::value, "");
 
 template<typename... Ix> arr data(const arr& a, Ix... index) {
     return arr(a.nbytes() - a.offset_at(index...), (const uint8_t *) a.data(index...));