merge(3p/immer): Subtree merge at 'ad3e3556d' as 'third_party/immer'

Change-Id: I9636a41ad44b4218293833fd3e9456d9b07c731b

third_party/immer/example/vector/gc.cpp

@@ -0,0 +1,37 @@
+//
+// immer: immutable data structures for C++
+// Copyright (C) 2016, 2017, 2018 Juan Pedro Bolivar Puente
+//
+// This software is distributed under the Boost Software License, Version 1.0.
+// See accompanying file LICENSE or copy at http://boost.org/LICENSE_1_0.txt
+//
+
+// include:example/start
+#include <immer/heap/gc_heap.hpp>
+#include <immer/heap/heap_policy.hpp>
+#include <immer/memory_policy.hpp>
+#include <immer/refcount/no_refcount_policy.hpp>
+#include <immer/vector.hpp>
+
+#include <iostream>
+
+// declare a memory policy for using a tracing garbage collector
+using gc_policy = immer::memory_policy<immer::heap_policy<immer::gc_heap>,
+                                       immer::no_refcount_policy,
+                                       immer::gc_transience_policy,
+                                       false>;
+
+// alias the vector type so we are not concerned about memory policies
+// in the places where we actually use it
+template <typename T>
+using my_vector = immer::vector<T, gc_policy>;
+
+int main()
+{
+    auto v =
+        my_vector<const char*>().push_back("hello, ").push_back("world!\n");
+
+    for (auto s : v)
+        std::cout << s;
+}
+// include:example/end