Accept abitrary containers and iterators for shape/strides

This adds support for constructing `buffer_info` and `array`s using
arbitrary containers or iterator pairs instead of requiring a vector.

This is primarily needed by PR #782 (which makes strides signed to
properly support negative strides, and will likely also make shape and
itemsize to avoid mixed integer issues), but also needs to preserve
backwards compatibility with 2.1 and earlier which accepts the strides
parameter as a vector of size_t's.

Rather than adding nearly duplicate constructors for each stride-taking
constructor, it seems nicer to simply allow any type of container (or
iterator pairs).  This works by replacing the existing vector arguments
with a new `detail::any_container` class that handles implicit
conversion of arbitrary containers into a vector of the desired type.
It can also be explicitly instantiated with a pair of iterators (e.g.
by passing {begin, end} instead of the container).

include/pybind11/buffer_info.h

@@ -7,7 +7,7 @@
     BSD-style license that can be found in the LICENSE file.
 */
 
-#pragma once 
+#pragma once
 
 #include "common.h"
 
@@ -26,25 +26,22 @@ struct buffer_info {
     buffer_info() { }
 
     buffer_info(void *ptr, size_t itemsize, const std::string &format, size_t ndim,
-                const std::vector<size_t> &shape, const std::vector<size_t> &strides)
-        : ptr(ptr), itemsize(itemsize), size(1), format(format),
-          ndim(ndim), shape(shape), strides(strides) {
+                detail::any_container<size_t> shape_in, detail::any_container<size_t> strides_in)
+    : ptr(ptr), itemsize(itemsize), size(1), format(format), ndim(ndim),
+      shape(std::move(shape_in)), strides(std::move(strides_in)) {
+        if (ndim != shape.size() || ndim != strides.size())
+            pybind11_fail("buffer_info: ndim doesn't match shape and/or strides length");
         for (size_t i = 0; i < ndim; ++i)
             size *= shape[i];
     }
 
     buffer_info(void *ptr, size_t itemsize, const std::string &format, size_t size)
-    : buffer_info(ptr, itemsize, format, 1, std::vector<size_t> { size },
-                  std::vector<size_t> { itemsize }) { }
+    : buffer_info(ptr, itemsize, format, 1, { size }, { itemsize }) { }
 
-    explicit buffer_info(Py_buffer *view, bool ownview = true)
-        : ptr(view->buf), itemsize((size_t) view->itemsize), size(1), format(view->format),
-          ndim((size_t) view->ndim), shape((size_t) view->ndim), strides((size_t) view->ndim), view(view), ownview(ownview) {
-        for (size_t i = 0; i < (size_t) view->ndim; ++i) {
-            shape[i] = (size_t) view->shape[i];
-            strides[i] = (size_t) view->strides[i];
-            size *= shape[i];
-        }
+    explicit buffer_info(Py_buffer *view, bool ownview_in = true)
+    : buffer_info(view->buf, (size_t) view->itemsize, view->format, (size_t) view->ndim,
+            {view->shape, view->shape + view->ndim}, {view->strides, view->strides + view->ndim}) {
+        ownview = ownview_in;
     }
 
     buffer_info(const buffer_info &) = delete;

include/pybind11/common.h

@@ -490,6 +490,12 @@ struct is_instantiation<Class, Class<Us...>> : std::true_type { };
 /// Check if T is std::shared_ptr<U> where U can be anything
 template <typename T> using is_shared_ptr = is_instantiation<std::shared_ptr, T>;
 
+/// Check if T looks like an input iterator
+template <typename T, typename = void> struct is_input_iterator : std::false_type {};
+template <typename T>
+struct is_input_iterator<T, void_t<decltype(*std::declval<T &>()), decltype(++std::declval<T &>())>>
+    : std::true_type {};
+
 /// Ignore that a variable is unused in compiler warnings
 inline void ignore_unused(const int *) { }
 
@@ -651,4 +657,46 @@ static constexpr auto const_ = std::true_type{};
 
 #endif // overload_cast
 
+NAMESPACE_BEGIN(detail)
+
+// Adaptor for converting arbitrary container arguments into a vector; implicitly convertible from
+// any standard container (or C-style array) supporting std::begin/std::end.
+template <typename T>
+class any_container {
+    std::vector<T> v;
+public:
+    any_container() = default;
+
+    // Can construct from a pair of iterators
+    template <typename It, typename = enable_if_t<is_input_iterator<It>::value>>
+    any_container(It first, It last) : v(first, last) { }
+
+    // Implicit conversion constructor from any arbitrary container type with values convertible to T
+    template <typename Container, typename = enable_if_t<std::is_convertible<decltype(*std::begin(std::declval<const Container &>())), T>::value>>
+    any_container(const Container &c) : any_container(std::begin(c), std::end(c)) { }
+
+    // initializer_list's aren't deducible, so don't get matched by the above template; we need this
+    // to explicitly allow implicit conversion from one:
+    template <typename TIn, typename = enable_if_t<std::is_convertible<TIn, T>::value>>
+    any_container(const std::initializer_list<TIn> &c) : any_container(c.begin(), c.end()) { }
+
+    // Avoid copying if given an rvalue vector of the correct type.
+    any_container(std::vector<T> &&v) : v(std::move(v)) { }
+
+    // Moves the vector out of an rvalue any_container
+    operator std::vector<T> &&() && { return std::move(v); }
+
+    // Dereferencing obtains a reference to the underlying vector
+    std::vector<T> &operator*() { return v; }
+    const std::vector<T> &operator*() const { return v; }
+
+    // -> lets you call methods on the underlying vector
+    std::vector<T> *operator->() { return &v; }
+    const std::vector<T> *operator->() const { return &v; }
+};
+
+NAMESPACE_END(detail)
+
+
+
 NAMESPACE_END(pybind11)

include/pybind11/eigen.h

@@ -201,18 +201,13 @@ template <typename Type_> struct EigenProps {
 // otherwise it'll make a copy.  writeable lets you turn off the writeable flag for the array.
 template <typename props> handle eigen_array_cast(typename props::Type const &src, handle base = handle(), bool writeable = true) {
     constexpr size_t elem_size = sizeof(typename props::Scalar);
-    std::vector<size_t> shape, strides;
-    if (props::vector) {
-        shape.push_back(src.size());
-        strides.push_back(elem_size * src.innerStride());
-    }
-    else {
-        shape.push_back(src.rows());
-        shape.push_back(src.cols());
-        strides.push_back(elem_size * src.rowStride());
-        strides.push_back(elem_size * src.colStride());
-    }
-    array a(std::move(shape), std::move(strides), src.data(), base);
+    array a;
+    if (props::vector)
+        a = array({ src.size() }, { elem_size * src.innerStride() }, src.data(), base);
+    else
+        a = array({ src.rows(), src.cols() }, { elem_size * src.rowStride(), elem_size * src.colStride() },
+                  src.data(), base);
+
     if (!writeable)
         array_proxy(a.ptr())->flags &= ~detail::npy_api::NPY_ARRAY_WRITEABLE_;
 

include/pybind11/numpy.h

@@ -455,12 +455,18 @@ public:
 
     array() : array(0, static_cast<const double *>(nullptr)) {}
 
-    array(const pybind11::dtype &dt, const std::vector<size_t> &shape,
-          const std::vector<size_t> &strides, const void *ptr = nullptr,
-          handle base = handle()) {
-        auto& api = detail::npy_api::get();
-        auto ndim = shape.size();
-        if (shape.size() != strides.size())
+    using ShapeContainer = detail::any_container<Py_intptr_t>;
+    using StridesContainer = detail::any_container<Py_intptr_t>;
+
+    // Constructs an array taking shape/strides from arbitrary container types
+    array(const pybind11::dtype &dt, ShapeContainer shape, StridesContainer strides,
+          const void *ptr = nullptr, handle base = handle()) {
+
+        if (strides->empty())
+            strides = default_strides(*shape, dt.itemsize());
+
+        auto ndim = shape->size();
+        if (ndim != strides->size())
             pybind11_fail("NumPy: shape ndim doesn't match strides ndim");
         auto descr = dt;
 
@@ -474,10 +480,9 @@ public:
                 flags = detail::npy_api::NPY_ARRAY_WRITEABLE_;
         }
 
+        auto &api = detail::npy_api::get();
         auto tmp = reinterpret_steal<object>(api.PyArray_NewFromDescr_(
-            api.PyArray_Type_, descr.release().ptr(), (int) ndim,
-            reinterpret_cast<Py_intptr_t *>(const_cast<size_t*>(shape.data())),
-            reinterpret_cast<Py_intptr_t *>(const_cast<size_t*>(strides.data())),
+            api.PyArray_Type_, descr.release().ptr(), (int) ndim, shape->data(), strides->data(),
             const_cast<void *>(ptr), flags, nullptr));
         if (!tmp)
             pybind11_fail("NumPy: unable to create array!");
@@ -491,27 +496,24 @@ public:
         m_ptr = tmp.release().ptr();
     }
 
-    array(const pybind11::dtype &dt, const std::vector<size_t> &shape,
-          const void *ptr = nullptr, handle base = handle())
-        : array(dt, shape, default_strides(shape, dt.itemsize()), ptr, base) { }
+    array(const pybind11::dtype &dt, ShapeContainer shape, const void *ptr = nullptr, handle base = handle())
+        : array(dt, std::move(shape), {}, ptr, base) { }
 
     array(const pybind11::dtype &dt, size_t count, const void *ptr = nullptr,
           handle base = handle())
-        : array(dt, std::vector<size_t>{ count }, ptr, base) { }
-
-    template<typename T> array(const std::vector<size_t>& shape,
-                               const std::vector<size_t>& strides,
-                               const T* ptr, handle base = handle())
-    : array(pybind11::dtype::of<T>(), shape, strides, (const void *) ptr, base) { }
+        : array(dt, ShapeContainer{{ count }}, ptr, base) { }
 
     template <typename T>
-    array(const std::vector<size_t> &shape, const T *ptr,
-          handle base = handle())
-        : array(shape, default_strides(shape, sizeof(T)), ptr, base) { }
+    array(ShapeContainer shape, StridesContainer strides, const T *ptr, handle base = handle())
+        : array(pybind11::dtype::of<T>(), std::move(shape), std::move(strides), ptr, base) { }
+
+    template <typename T>
+    array(ShapeContainer shape, const T *ptr, handle base = handle())
+        : array(std::move(shape), {}, ptr, base) { }
 
     template <typename T>
     array(size_t count, const T *ptr, handle base = handle())
-        : array(std::vector<size_t>{ count }, ptr, base) { }
+        : array({{ count }}, ptr, base) { }
 
     explicit array(const buffer_info &info)
     : array(pybind11::dtype(info), info.shape, info.strides, info.ptr) { }
@@ -673,9 +675,9 @@ protected:
             throw std::domain_error("array is not writeable");
     }
 
-    static std::vector<size_t> default_strides(const std::vector<size_t>& shape, size_t itemsize) {
+    static std::vector<Py_intptr_t> default_strides(const std::vector<Py_intptr_t>& shape, size_t itemsize) {
         auto ndim = shape.size();
-        std::vector<size_t> strides(ndim);
+        std::vector<Py_intptr_t> strides(ndim);
         if (ndim) {
             std::fill(strides.begin(), strides.end(), itemsize);
             for (size_t i = 0; i < ndim - 1; i++)
@@ -731,14 +733,11 @@ public:
 
     explicit array_t(const buffer_info& info) : array(info) { }
 
-    array_t(const std::vector<size_t> &shape,
-            const std::vector<size_t> &strides, const T *ptr = nullptr,
-            handle base = handle())
-        : array(shape, strides, ptr, base) { }
+    array_t(ShapeContainer shape, StridesContainer strides, const T *ptr = nullptr, handle base = handle())
+        : array(std::move(shape), std::move(strides), ptr, base) { }
 
-    explicit array_t(const std::vector<size_t> &shape, const T *ptr = nullptr,
-            handle base = handle())
-        : array(shape, ptr, base) { }
+    explicit array_t(ShapeContainer shape, const T *ptr = nullptr, handle base = handle())
+        : array(std::move(shape), ptr, base) { }
 
     explicit array_t(size_t count, const T *ptr = nullptr, handle base = handle())
         : array(count, ptr, base) { }

tests/test_numpy_array.cpp

@@ -13,7 +13,6 @@
 #include <pybind11/stl.h>
 
 #include <cstdint>
-#include <vector>
 
 using arr = py::array;
 using arr_t = py::array_t<uint16_t, 0>;
@@ -119,8 +118,8 @@ test_initializer numpy_array([](py::module &m) {
     sm.def("wrap", [](py::array a) {
         return py::array(
             a.dtype(),
-            std::vector<size_t>(a.shape(), a.shape() + a.ndim()),
-            std::vector<size_t>(a.strides(), a.strides() + a.ndim()),
+            {a.shape(), a.shape() + a.ndim()},
+            {a.strides(), a.strides() + a.ndim()},
             a.data(),
             a
         );