From 8ac881a544e8fc7f85d78132610fce1b696d2025 Mon Sep 17 00:00:00 2001
From: Linus Jahn <lnj@kaidan.im>
Date: Sat, 28 Jan 2023 17:08:05 +0100
Subject: Task/Promise: Don't allow abstract types

Supporting abstract types only has little advantages and we might want
to store the result by value later.
---
 src/base/QXmppPromise.h | 5 +++--
 src/base/QXmppTask.h    | 9 +--------
 2 files changed, 4 insertions(+), 10 deletions(-)

(limited to 'src/base')

diff --git a/src/base/QXmppPromise.h b/src/base/QXmppPromise.h
index 09bc5bcb..91443c7f 100644
--- a/src/base/QXmppPromise.h
+++ b/src/base/QXmppPromise.h
@@ -21,6 +21,7 @@
 template<typename T>
 class QXmppPromise
 {
+    static_assert(!std::is_abstract_v<T>);
 public:
     template<typename U = T, std::enable_if_t<std::is_void_v<U>> * = nullptr>
     QXmppPromise()
@@ -43,7 +44,7 @@ public:
 #ifdef QXMPP_DOC
     void reportFinished(T &&value)
 #else
-    template<typename U, std::enable_if_t<!std::is_void_v<T> && std::is_base_of_v<T, U>> * = nullptr>
+    template<typename U, std::enable_if_t<!std::is_void_v<T> && std::is_same_v<T, U>> * = nullptr>
     void finish(U &&value)
 #endif
     {
@@ -59,7 +60,7 @@ public:
     }
 
     /// \cond
-    template<typename U, std::enable_if_t<!std::is_void_v<T> && std::is_constructible_v<T, U> && !std::is_base_of_v<T, U>> * = nullptr>
+    template<typename U, std::enable_if_t<!std::is_void_v<T> && std::is_constructible_v<T, U> && !std::is_same_v<T, U>> * = nullptr>
     void finish(U &&value)
     {
         Q_ASSERT(!d.isFinished());
diff --git a/src/base/QXmppTask.h b/src/base/QXmppTask.h
index 141cf10e..84ba8a33 100644
--- a/src/base/QXmppTask.h
+++ b/src/base/QXmppTask.h
@@ -50,10 +50,6 @@ private:
 ///
 /// Tasks are generated by QXmppPromise and can be handled using QXmppTask::then().
 ///
-/// It supports abstract types, i.e. you can create a QXmppTask<QXmppStanza> and report MyIq
-/// (derived from QXmppStanza) to it and when handling the result it is possible to cast the result
-/// back to MyIq.
-///
 /// Unlike QFuture, this is not thread-safe. This avoids the need to do mutex locking at every
 /// access though.
 ///
@@ -177,10 +173,7 @@ public:
     ///
     /// Moves the result of the operation out of the task.
     ///
-    /// Since this returns by value, you will not be able to cast the result to derived types. Use
-    /// result() for read-only access or register a handler function using then().
-    ///
-    /// \warning This can only be used once the operation is finished.
+    /// \warning This can only be used once and only after the operation has finished.
     ///
 #ifdef QXMPP_DOC
     [[nodiscard]] T takeResult()
-- 
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