From 34ad55bb294c4d921a4ece8b9fd8305d038db9ac Mon Sep 17 00:00:00 2001
From: Chocobo1 <Chocobo1@users.noreply.github.com>
Date: Tue, 7 Oct 2025 02:12:27 +0800
Subject: [PATCH] Avoid duplicate lookup

In C++20 `std::views::transform()` followed by `std::views::filter()` has a nasty effect of
invoking transformation function twice.
Note that there will be a `std::views::cache_latest()` in C++26 to
address this issue.

Ref:
https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p2760r1.html#cache_last
https://stackoverflow.com/questions/64199664/why-c-ranges-transform-filter-calls-transform-twice-for-values-that-match

PR #23343.
---
 src/base/bittorrent/sessionimpl.cpp | 15 +++++++++------
 1 file changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/base/bittorrent/sessionimpl.cpp b/src/base/bittorrent/sessionimpl.cpp
index 1d65baa67..18c0c1b30 100644
--- a/src/base/bittorrent/sessionimpl.cpp
+++ b/src/base/bittorrent/sessionimpl.cpp
@@ -5923,12 +5923,15 @@ TorrentImpl *SessionImpl::getTorrent(const lt::torrent_handle &nativeHandle) con
 
 QList<TorrentImpl *> SessionImpl::getQueuedTorrentsByID(const QList<TorrentID> &torrentIDs) const
 {
-    auto torrents = torrentIDs
-            | std::views::transform([this](const TorrentID &torrentID) { return m_torrents.value(torrentID); })
-            | std::views::filter([](const TorrentImpl *torrent) { return torrent && (torrent->queuePosition() >= 0); });
-
-    QList<TorrentImpl *> queuedTorrents = {torrents.begin(), torrents.end()};
-    std::ranges::sort(queuedTorrents, std::less<>(), &TorrentImpl::queuePosition);
+    QList<TorrentImpl *> queuedTorrents;
+    queuedTorrents.reserve(torrentIDs.size());
+    for (const TorrentID &torrentID : torrentIDs)
+    {
+        TorrentImpl *torrent = m_torrents.value(torrentID);
+        if (torrent && (torrent->queuePosition() >= 0))
+            queuedTorrents.push_back(torrent);
+    }
+    std::ranges::sort(queuedTorrents, std::less(), &TorrentImpl::queuePosition);
     return queuedTorrents;
 }