Added 'bind_set(...)' to std_binds

Based off github.com/beatmax's solution.

include/pybind11/stl_bind.h

@@ -569,6 +569,82 @@ class_<Vector, holder_type> bind_vector(handle scope, std::string const &name, A
     return cl;
 }
 
+//
+// std::set
+//
+template <typename Set, typename holder_type = std::unique_ptr<Set>, typename... Args>
+class_<Set, holder_type> bind_set(handle scope, std::string const &name, Args &&...args) {
+    using Class_ = class_<Set, holder_type>;
+    using T = typename Set::value_type;
+    using ItType = typename Set::iterator;
+
+    auto vtype_info = detail::get_type_info(typeid(T));
+    bool local = !vtype_info || vtype_info->module_local;
+
+    Class_ cl(scope, name.c_str(), pybind11::module_local(local), std::forward<Args>(args)...);
+    cl.def(init<>());
+    cl.def(init<const Set &>(), "Copy constructor");
+    cl.def(init([](iterable it) {
+        auto s = std::unique_ptr<Set>(new Set());
+        for (handle h : it)
+            s->insert(h.cast<T>());
+        return s.release();
+    }));
+    cl.def(self == self);
+    cl.def(self != self);
+    cl.def(
+        "remove",
+        [](Set &s, const T &x) {
+            auto p = s.find(x);
+            if (p != s.end())
+                s.erase(p);
+            else
+                throw value_error();
+        },
+        arg("x"),
+        "Remove the item from the set whose value is x. "
+        "It is an error if there is no such item.");
+    cl.def(
+        "__contains__",
+        [](const Set &s, const T &x) { return s.find(x) != s.end(); },
+        arg("x"),
+        "Return true if the container contains ``x``.");
+    cl.def(
+        "add",
+        [](Set &s, const T &value) { s.insert(value); },
+        arg("x"),
+        "Add an item to the set.");
+    cl.def("clear", [](Set &s) { s.clear(); }, "Clear the contents.");
+    cl.def(
+        "__iter__",
+        [](Set &s) {
+            return make_iterator<return_value_policy::copy, ItType, ItType, T>(s.begin(), s.end());
+        },
+        keep_alive<0, 1>() /* Essential: keep set alive while iterator exists */
+    );
+    cl.def(
+        "__repr__",
+        [name](Set &s) {
+            std::ostringstream os;
+            os << name << '{';
+            for (auto it = s.begin(); it != s.end(); ++it) {
+                if (it != s.begin())
+                    os << ", ";
+                os << *it;
+            }
+            os << '}';
+            return os.str();
+        },
+        "Return the canonical string representation of this set.");
+    cl.def(
+        "__bool__",
+        [](const Set &s) -> bool { return !s.empty(); },
+        "Check whether the set is nonempty");
+    cl.def("__len__", &Set::size);
+
+    return cl;
+}
+
 //
 // std::map, std::unordered_map
 //

tests/test_stl_binders.cpp

@@ -14,6 +14,7 @@
 
 #include <deque>
 #include <map>
+#include <set>
 #include <unordered_map>
 #include <vector>
 
@@ -183,6 +184,9 @@ TEST_SUBMODULE(stl_binders, m) {
     py::bind_vector<std::vector<El>>(m, "VectorEl");
     py::bind_vector<std::vector<std::vector<El>>>(m, "VectorVectorEl");
 
+    // test_set_int
+    py::bind_set<std::set<int>>(m, "SetInt");
+
     // test_map_string_double
     py::bind_map<std::map<std::string, double>>(m, "MapStringDouble");
     py::bind_map<std::unordered_map<std::string, double>>(m, "UnorderedMapStringDouble");

tests/test_stl_binders.py

@@ -149,6 +149,29 @@ def test_vector_custom():
     assert str(vv_b) == "VectorEl[El{1}, El{2}]"
 
 
+def test_set_int():
+    s_a = m.SetInt()
+    s_b = m.SetInt()
+
+    assert len(s_a) == 0
+    assert s_a == s_b
+
+    s_a.add(1)
+
+    assert 1 in s_a
+    assert str(s_a) == "SetInt{1}"
+    assert s_a != s_b
+
+    for i in range(5):
+        s_a.add(i)
+
+    assert sorted(s_a) == [0, 1, 2, 3, 4]
+
+    s_a.clear()
+    assert len(s_a) == 0
+    assert str(s_a) == "SetInt{}"
+
+
 def test_map_string_double():
     mm = m.MapStringDouble()
     mm["a"] = 1