From af051f9be230f06eba587c25d56837fb48fcc9ee Mon Sep 17 00:00:00 2001
From: Marc Mutz <marc.mutz@qt.io>
Date: Wed, 14 Feb 2024 09:52:22 +0100
Subject: [PATCH] QVarLengthArray: re-publish Prealloc as a nested
 PreallocatedSize

This gives users of the class easy access to the Prealloc template
argument, without having to write a pattern-matcher like

   template <typename T>
   constexpr qsizetype preallocated_size_v;
   template <typename T, qsizetype N>
   constexpr qsizetype preallocated_size_v<QVarLengthArray<T,N>> = N;

first.

[ChangeLog][QtCore][QVarLengthArray] Added PreallocatedSize nested
constant, equal to the Prealloc template argument.

Change-Id: I928eaa5e62967445cdd7b0c2759567483fdb8997
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
---
 src/corelib/tools/qvarlengtharray.h                    |  2 ++
 src/corelib/tools/qvarlengtharray.qdoc                 |  9 +++++++++
 .../tools/qvarlengtharray/tst_qvarlengtharray.cpp      | 10 ++++++++++
 3 files changed, 21 insertions(+)

diff --git a/src/corelib/tools/qvarlengtharray.h b/src/corelib/tools/qvarlengtharray.h
index db04b683b1..8fa6da9a9a 100644
--- a/src/corelib/tools/qvarlengtharray.h
+++ b/src/corelib/tools/qvarlengtharray.h
@@ -278,6 +278,8 @@ class QVarLengthArray
     template <typename InputIterator>
     using if_input_iterator = QtPrivate::IfIsInputIterator<InputIterator>;
 public:
+    static constexpr qsizetype PreallocatedSize = Prealloc;
+
     using size_type = typename Base::size_type;
     using value_type = typename Base::value_type;
     using pointer = typename Base::pointer;
diff --git a/src/corelib/tools/qvarlengtharray.qdoc b/src/corelib/tools/qvarlengtharray.qdoc
index e6d7cc16ec..4ebbcc43dc 100644
--- a/src/corelib/tools/qvarlengtharray.qdoc
+++ b/src/corelib/tools/qvarlengtharray.qdoc
@@ -462,6 +462,15 @@
     \a defaultValue.
 */
 
+/*
+    \var QVarLengthArray::PreallocatedSize
+    \since 6.8
+
+    The same value as the \c{Prealloc} template argument. Provided for easier
+    access compared to manually extracting the value from the template
+    argument.
+*/
+
 /*!
     \typedef QVarLengthArray::size_type
     \since 4.7
diff --git a/tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp b/tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp
index dcee8fd705..6a92663bc4 100644
--- a/tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp
+++ b/tests/auto/corelib/tools/qvarlengtharray/tst_qvarlengtharray.cpp
@@ -66,6 +66,7 @@ private slots:
     void sizeConstructor_QString() { sizeConstructor<QString>(); }
     void sizeConstructor_NonCopyable() { sizeConstructor<NonCopyable>(); }
     void append();
+    void preallocatedSize();
 #if QT_DEPRECATED_SINCE(6, 3)
     void prepend();
 #endif
@@ -194,6 +195,15 @@ void tst_QVarLengthArray::append()
     v2.append(5);
 }
 
+void tst_QVarLengthArray::preallocatedSize()
+{
+    // The default is 256:
+    static_assert(QVarLengthArray<int>::PreallocatedSize == 256);
+    // Otherwise, whatever was given as template argument:
+    static_assert(QVarLengthArray<int, 42>::PreallocatedSize == 42);
+    static_assert(QVarLengthArray<int, 1'000'000>::PreallocatedSize == 1'000'000);
+}
+
 #if QT_DEPRECATED_SINCE(6, 3)
 QT_WARNING_PUSH
 QT_WARNING_DISABLE_DEPRECATED