From 0dd491fbd189baaabadcab2344a05e3cf3898287 Mon Sep 17 00:00:00 2001
From: Kitsune Ral <Kitsune-Ral@users.sf.net>
Date: Sat, 2 Jun 2018 13:32:47 +0900
Subject: csapi: Use Omittable<> container instead of intrusive 'omitted' field

Also: use the latest feature of GTAD, +set/+on, to make gtad.yaml more compact.
---
 lib/converters.h | 63 +++++++++++++++++++++++++++++++++++++++++++++-----------
 1 file changed, 51 insertions(+), 12 deletions(-)

(limited to 'lib/converters.h')

diff --git a/lib/converters.h b/lib/converters.h
index fb1da6d7..916124a6 100644
--- a/lib/converters.h
+++ b/lib/converters.h
@@ -45,6 +45,47 @@ namespace std
 
 namespace QMatrixClient
 {
+    struct NoneTag {};
+    constexpr NoneTag none {};
+
+    /** A crude substitute for `optional` while we're not C++17
+     *
+     * Only works with default-constructible types.
+     */
+    template <typename T>
+    class Omittable
+    {
+        public:
+            explicit Omittable() : Omittable(none) { }
+            Omittable(NoneTag) : _omitted(true) { }
+            Omittable(const T& val) : _value(val), _omitted(false) { }
+            Omittable(T&& val) : _value(std::move(val)), _omitted(false) { }
+            Omittable<T>& operator=(const T& val)
+            {
+                _value = val;
+                _omitted = false;
+                return *this;
+            }
+            Omittable<T>& operator=(T&& val)
+            {
+                _value = std::move(val);
+                _omitted = false;
+                return *this;
+            }
+
+            bool omitted() const { return _omitted; }
+            const T& value() const { return _value; }
+            T& value() { return _value; }
+            T&& release() { _omitted = true; return std::move(value); }
+
+            operator bool() const { return !_omitted; }
+
+        private:
+            T _value;
+            bool _omitted;
+    };
+
+
     // This catches anything implicitly convertible to QJsonValue/Object/Array
     inline QJsonValue toJson(const QJsonValue& val) { return val; }
     inline QJsonObject toJson(const QJsonObject& o) { return o; }
@@ -99,6 +140,16 @@ namespace QMatrixClient
         return json;
     }
 
+    template <typename T>
+    inline auto toJson(const Omittable<T>& omittable)
+        -> decltype(toJson(omittable.value()))
+    {
+        if (omittable)
+            return toJson(omittable.value());
+
+        return {};
+    }
+
 #if 0
     template <typename T>
     inline auto toJson(const optional<T>& optVal)
@@ -287,16 +338,4 @@ namespace QMatrixClient
         _impl::AddNode<std::conditional_t<Force, QJsonValue, decltype(json)>>
                 ::impl(o, std::move(key), std::move(json));
     }
-
-    /** Construct an "omitted" value of a given type
-     * This is a workaround for the time being while we're not C++17 and
-     * cannot use `optional`.
-     */
-    template <typename T>
-    inline T omitted()
-    {
-        T val;
-        val.omitted = true;
-        return val;
-    }
 }  // namespace QMatrixClient
-- 
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