Adds type_caster support for std::deque. (#1609)

* Adds std::deque to the types supported by list_caster in stl.h.
* Adds a new test_deque test in test_stl.{py,cpp}.
* Updates the documentation to include std::deque as a default
  supported type.

docs/advanced/cast/stl.rst

@@ -5,7 +5,7 @@ Automatic conversion
 ====================
 
 When including the additional header file :file:`pybind11/stl.h`, conversions
-between ``std::vector<>``/``std::list<>``/``std::array<>``,
+between ``std::vector<>``/``std::deque<>``/``std::list<>``/``std::array<>``,
 ``std::set<>``/``std::unordered_set<>``, and
 ``std::map<>``/``std::unordered_map<>`` and the Python ``list``, ``set`` and
 ``dict`` data structures are automatically enabled. The types ``std::pair<>``

include/pybind11/stl.h

@@ -16,6 +16,7 @@
 #include <unordered_map>
 #include <iostream>
 #include <list>
+#include <deque>
 #include <valarray>
 
 #if defined(_MSC_VER)
@@ -185,6 +186,9 @@ public:
 template <typename Type, typename Alloc> struct type_caster<std::vector<Type, Alloc>>
  : list_caster<std::vector<Type, Alloc>, Type> { };
 
+template <typename Type, typename Alloc> struct type_caster<std::deque<Type, Alloc>>
+ : list_caster<std::deque<Type, Alloc>, Type> { };
+
 template <typename Type, typename Alloc> struct type_caster<std::list<Type, Alloc>>
  : list_caster<std::list<Type, Alloc>, Type> { };
 

tests/test_stl.cpp

@@ -63,6 +63,10 @@ TEST_SUBMODULE(stl, m) {
     static std::vector<RValueCaster> lvv{2};
     m.def("cast_ptr_vector", []() { return &lvv; });
 
+    // test_deque
+    m.def("cast_deque", []() { return std::deque<int>{1}; });
+    m.def("load_deque", [](const std::deque<int> &v) { return v.at(0) == 1 && v.at(1) == 2; });
+
     // test_array
     m.def("cast_array", []() { return std::array<int, 2> {{1 , 2}}; });
     m.def("load_array", [](const std::array<int, 2> &a) { return a[0] == 1 && a[1] == 2; });

tests/test_stl.py

@@ -23,6 +23,15 @@ def test_vector(doc):
     assert m.cast_ptr_vector() == ["lvalue", "lvalue"]
 
 
+def test_deque(doc):
+    """std::deque <-> list"""
+    lst = m.cast_deque()
+    assert lst == [1]
+    lst.append(2)
+    assert m.load_deque(lst)
+    assert m.load_deque(tuple(lst))
+
+
 def test_array(doc):
     """std::array <-> list"""
     lst = m.cast_array()