Short live q20::copy{,_n,_if}!

All they do is add constexpr.

Use them in QOffsetStringArray where they replace a custom
implementation, except, as usual, the custom implementation does one
tiny thing more, so not all uses can be replaced.

Explicitly not use it in QStaticByteArrayMatcher to not cause
conflicts with the introduction of QStaticLatin1StringMatcher.

Pick-to: 6.4
Change-Id: I3c102a7e934a1d7d5fae4cbc629a4fabf2c47c92
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Mårten Nordheim <marten.nordheim@qt.io>

src/corelib/global/q20algorithm.h

@@ -27,11 +27,53 @@
 QT_BEGIN_NAMESPACE
 
 namespace q20 {
-// like std::is_sorted{,_until} (ie. constexpr)
+// like std::is_sorted{,_until}, std::copy (ie. constexpr)
 #ifdef __cpp_lib_constexpr_algorithms
+using std::copy;
+using std::copy_if;
+using std::copy_n;
 using std::is_sorted_until;
 using std::is_sorted;
 #else
+template <typename InputIterator, typename OutputIterator>
+constexpr OutputIterator
+copy(InputIterator first, InputIterator last, OutputIterator dest)
+{
+    while (first != last) {
+        *dest = *first;
+        ++first;
+        ++dest;
+    }
+    return dest;
+}
+
+template <typename InputIterator, typename OutputIterator, typename UnaryPredicate>
+constexpr OutputIterator
+copy_if(InputIterator first, InputIterator last, OutputIterator dest, UnaryPredicate pred)
+{
+    while (first != last) {
+        if (pred(*first)) {
+            *dest = *first;
+            ++dest;
+        }
+        ++first;
+    }
+    return dest;
+}
+
+template <typename InputIterator, typename Size, typename OutputIterator>
+constexpr OutputIterator
+copy_n(InputIterator first, Size n, OutputIterator dest)
+{
+    while (n > Size{0}) {
+        *dest = *first;
+        ++first;
+        ++dest;
+        --n;
+    }
+    return dest;
+}
+
 template <typename ForwardIterator, typename BinaryPredicate = std::less<>>
 constexpr ForwardIterator
 is_sorted_until(ForwardIterator first, ForwardIterator last, BinaryPredicate p = {})

src/corelib/tools/qoffsetstringarray_p.h

@@ -20,6 +20,7 @@
 
 #include <QByteArrayView>
 
+#include <QtCore/q20algorithm.h>
 #include <array>
 #include <limits>
 #include <string_view>
@@ -100,7 +101,7 @@ constexpr auto makeStaticString(Extractor extract, const T &... entries)
     const char *strings[] = { extract(entries).operator const char *()... };
     size_t lengths[] = { sizeof(extract(T{}))... };
     for (size_t i = 0; i < std::size(strings); ++i) {
-        copyData(strings[i], lengths[i], result.begin() + offset);
+        q20::copy_n(strings[i], lengths[i], result.begin() + offset);
         offset += lengths[i];
     }
     return result;
@@ -110,7 +111,7 @@ template <size_t N> struct StaticString
 {
     char value[N] = {};
     constexpr StaticString() = default;
-    constexpr StaticString(const char (&s)[N])  { copyData(s, N, value); }
+    constexpr StaticString(const char (&s)[N])  { q20::copy_n(s, N, value); }
     constexpr operator const char *() const     { return value; }
 };