From 19e552861f9321a9c73bc4d3aa5102387772a321 Mon Sep 17 00:00:00 2001
From: Minijackson <minijackson@riseup.net>
Date: Thu, 8 Mar 2018 10:25:27 +0100
Subject: Use placement new in Expected when constructing objects

---
 framework/src/errors.h | 44 ++++++++++++++++++++++++++------------------
 1 file changed, 26 insertions(+), 18 deletions(-)

diff --git a/framework/src/errors.h b/framework/src/errors.h
index 9c48f32a..5ee1a667 100644
--- a/framework/src/errors.h
+++ b/framework/src/errors.h
@@ -84,45 +84,48 @@ struct StorageBase
 protected:
     // Rule of 5 {{{
 
-    constexpr void copyPartFromOther(const StorageBase &other)
+    StorageBase(const StorageBase &other) : mIsValue(other.mIsValue)
     {
+        // This is a constructor, you have to construct object, not assign them
+        // (hence the placement new)
         if (mIsValue) {
-            mValue = other.mValue;
+            new (std::addressof(mValue)) Type(other.mValue);
         } else {
-            mError = other.mError;
+            new (std::addressof(mError)) Unexpected<Error>(other.mError);
         }
     }
 
-    void movePartFromOther(StorageBase &&other)
+    StorageBase(StorageBase &&other) : mIsValue(other.mIsValue)
     {
+        // This is a constructor, you have to construct object, not assign them
+        // (hence the placement new)
         if (mIsValue) {
-            mValue = std::move(other.mValue);
+            new (std::addressof(mValue)) Type(std::move(other.mValue));
         } else {
-            mError = std::move(other.mError);
+            new (std::addressof(mError)) Unexpected<Error>(std::move(other.mError));
         }
     }
 
-    StorageBase(const StorageBase &other) : mIsValue(other.mIsValue)
-    {
-        copyPartFromOther(other);
-    }
-
-    StorageBase(StorageBase &&other) : mIsValue(other.mIsValue)
-    {
-        movePartFromOther(std::move(other));
-    }
-
     constexpr StorageBase &operator=(const StorageBase &other)
     {
         mIsValue = other.mIsValue;
-        copyPartFromOther(other);
+        if (mIsValue) {
+            mValue = other.mValue;
+        } else {
+            mError = other.mError;
+        }
         return *this;
     }
 
     constexpr StorageBase &operator=(StorageBase &&other)
     {
+        this->~StorageBase();
         mIsValue = other.mIsValue;
-        movePartFromOther(other);
+        if (mIsValue) {
+            mValue = std::move(other.mValue);
+        } else {
+            mError = std::move(other.mError);
+        }
         return *this;
     }
 
@@ -216,6 +219,11 @@ struct ExpectedBase : detail::Storage<Error, Type>
         Q_ASSERT(this->mIsValue);
         return this->mValue;
     }
+    Type &&value() &&
+    {
+        Q_ASSERT(this->mIsValue);
+        return std::move(this->mValue);
+    }
 };
 
 // Write functions here when dev API related and when Type == void
-- 
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