1 files changed, 129 insertions, 0 deletions
diff --git a/src/boost/libs/hana/example/misc/from_json.cpp b/src/boost/libs/hana/example/misc/from_json.cpp
new file mode 100644
index 00000000..a28cac1e
--- /dev/null
+++ b/src/boost/libs/hana/example/misc/from_json.cpp
@@ -0,0 +1,129 @@
+// Copyright Louis Dionne 2013-2017
+// Distributed under the Boost Software License, Version 1.0.
+// (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
+
+#include <boost/hana/assert.hpp>
+#include <boost/hana/at.hpp>
+#include <boost/hana/at_key.hpp>
+#include <boost/hana/concept/sequence.hpp>
+#include <boost/hana/concept/struct.hpp>
+#include <boost/hana/define_struct.hpp>
+#include <boost/hana/for_each.hpp>
+#include <boost/hana/keys.hpp>
+#include <boost/hana/length.hpp>
+#include <boost/hana/not_equal.hpp>
+#include <boost/hana/tuple.hpp>
+
+#include <iostream>
+#include <limits>
+#include <sstream>
+#include <string>
+#include <type_traits>
+namespace hana = boost::hana;
+
+
+struct Car {
+    BOOST_HANA_DEFINE_STRUCT(Car,
+        (std::string, brand),
+        (std::string, model)
+    );
+};
+
+struct Person {
+    BOOST_HANA_DEFINE_STRUCT(Person,
+        (std::string, name),
+        (std::string, last_name),
+        (int, age)
+    );
+};
+
+template <typename T>
+  std::enable_if_t<std::is_same<T, int>::value,
+T> from_json(std::istream& in) {
+    T result;
+    in >> result;
+    return result;
+}
+
+template <typename T>
+  std::enable_if_t<std::is_same<T, std::string>::value,
+T> from_json(std::istream& in) {
+    char quote;
+    in >> quote;
+
+    T result;
+    char c;
+    while (in.get(c) && c != '"') {
+        result += c;
+    }
+    return result;
+}
+
+
+template <typename T>
+  std::enable_if_t<hana::Struct<T>::value,
+T> from_json(std::istream& in) {
+    T result;
+    char brace;
+    in >> brace;
+
+    // CAREFUL: This only works if the input JSON contains the fields in the
+    //          same order as the struct declares them.
+    hana::for_each(hana::keys(result), [&](auto key) {
+        in.ignore(std::numeric_limits<std::streamsize>::max(), ':');
+        auto& member = hana::at_key(result, key);
+        using Member = std::remove_reference_t<decltype(member)>;
+        member = from_json<Member>(in);
+    });
+    in >> brace;
+    return result;
+}
+
+template <typename Xs>
+  std::enable_if_t<hana::Sequence<Xs>::value,
+Xs> from_json(std::istream& in) {
+    Xs result;
+    char bracket;
+    in >> bracket;
+    hana::length(result).times.with_index([&](auto i) {
+        if (i != 0u) {
+            char comma;
+            in >> comma;
+        }
+
+        auto& element = hana::at(result, i);
+        using Element = std::remove_reference_t<decltype(element)>;
+        element = from_json<Element>(in);
+    });
+    in >> bracket;
+    return result;
+}
+
+
+int main() {
+    std::istringstream json(R"EOS(
+        [
+            {
+                "name": "John",
+                "last_name": "Doe",
+                "age": 30
+            },
+            {
+                "brand": "BMW",
+                "model": "Z3"
+            },
+            {
+                "brand": "Audi",
+                "model": "A4"
+            }
+        ]
+    )EOS");
+
+    auto actual = from_json<hana::tuple<Person, Car, Car>>(json);
+
+    auto expected = hana::make_tuple(Person{"John", "Doe", 30},
+                                     Car{"BMW", "Z3"},
+                                     Car{"Audi", "A4"});
+
+    BOOST_HANA_RUNTIME_CHECK(actual == expected);
+}