Long live Q_IMPLICIT!

C++20 will give us explicit(bool). While we can't use it just yet
in its full potential, we can introduce a macro to start marking
our implicit conversions (aka `explicit(false)`), removing the need
for /* implicit */-like comments.

Port a few usages to it.

Change-Id: I336d5e4c8d51d8329627900d1059e59062c5cafd
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
Reviewed-by: Lars Knoll <lars.knoll@qt.io>

5 files changed, 25 insertions, 19 deletions

diff --git a/src/corelib/global/qglobal.h b/src/corelib/global/qglobal.h
index b22e2f526a..3e32a4815a 100644
--- a/src/corelib/global/qglobal.h
+++ b/src/corelib/global/qglobal.h
@@ -1042,6 +1042,12 @@ constexpr T qExchange(T &t, U &&newValue)
     return old;
 }
 
+#ifdef __cpp_conditional_explicit
+#define Q_IMPLICIT explicit(false)
+#else
+#define Q_IMPLICIT
+#endif
+
 #ifndef QT_NO_FOREACH
 
 namespace QtPrivate {
diff --git a/src/corelib/global/qnamespace.h b/src/corelib/global/qnamespace.h
index 2cbe482fd4..d19f50512a 100644
--- a/src/corelib/global/qnamespace.h
+++ b/src/corelib/global/qnamespace.h
@@ -1873,7 +1873,7 @@ class QKeyCombination
     int combination;
 
 public:
-    constexpr /* implicit */ QKeyCombination(Qt::Key key = Qt::Key_unknown) noexcept
+    constexpr Q_IMPLICIT QKeyCombination(Qt::Key key = Qt::Key_unknown) noexcept
         : combination(int(key))
     {}
 
@@ -1909,7 +1909,7 @@ public:
 
 #if QT_DEPRECATED_SINCE(6, 0)
     QT_DEPRECATED_VERSION_X(6, 0, "Use QKeyCombination instead of int")
-    constexpr /* implicit */ operator int() const noexcept
+    constexpr Q_IMPLICIT operator int() const noexcept
     {
         return combination;
     }
diff --git a/src/corelib/kernel/qsocketnotifier.h b/src/corelib/kernel/qsocketnotifier.h
index 528f58a1e1..b8a5cc542a 100644
--- a/src/corelib/kernel/qsocketnotifier.h
+++ b/src/corelib/kernel/qsocketnotifier.h
@@ -102,14 +102,14 @@ public:
 #define Q_DECL_CONSTEXPR_NOT_WIN Q_DECL_CONSTEXPR
 #endif
 
-    /* implicit */ Q_DECL_CONSTEXPR_NOT_WIN
+    Q_DECL_CONSTEXPR_NOT_WIN Q_IMPLICIT
     QSocketDescriptor(DescriptorType descriptor = DescriptorType(-1)) noexcept : sockfd(descriptor)
     {
     }
 
 #if defined(Q_OS_WIN) || defined(Q_QDOC)
-    /* implicit */ QSocketDescriptor(qintptr desc) noexcept : sockfd(DescriptorType(desc)) {}
-    operator qintptr() const noexcept { return qintptr(sockfd); }
+    Q_IMPLICIT QSocketDescriptor(qintptr desc) noexcept : sockfd(DescriptorType(desc)) {}
+    Q_IMPLICIT operator qintptr() const noexcept { return qintptr(sockfd); }
     Q_DECL_CONSTEXPR Qt::HANDLE winHandle() const noexcept { return sockfd; }
 #endif
     Q_DECL_CONSTEXPR operator DescriptorType() const noexcept { return sockfd; }
diff --git a/src/corelib/text/qchar.h b/src/corelib/text/qchar.h
index 5d807d97a3..96a99aa1d3 100644
--- a/src/corelib/text/qchar.h
+++ b/src/corelib/text/qchar.h
@@ -94,28 +94,28 @@ public:
         LastValidCodePoint = 0x10ffff
     };
 
-    constexpr QChar() noexcept : ucs(0) {}
-    constexpr QChar(ushort rc) noexcept : ucs(rc) {}
-    constexpr QChar(uchar c, uchar r) noexcept : ucs(char16_t((r << 8) | c)) {}
-    constexpr QChar(short rc) noexcept : ucs(char16_t(rc)) {}
-    constexpr QChar(uint rc) noexcept : ucs(char16_t(rc & 0xffff)) {}
-    constexpr QChar(int rc) noexcept : ucs(char16_t(rc & 0xffff)) {}
-    constexpr QChar(SpecialCharacter s) noexcept : ucs(char16_t(s)) {} // implicit
-    constexpr QChar(QLatin1Char ch) noexcept : ucs(ch.unicode()) {} // implicit
-    constexpr QChar(char16_t ch) noexcept : ucs(ch) {} // implicit
+    constexpr Q_IMPLICIT QChar() noexcept : ucs(0) {}
+    constexpr Q_IMPLICIT QChar(ushort rc) noexcept : ucs(rc) {}
+    constexpr Q_IMPLICIT QChar(uchar c, uchar r) noexcept : ucs(char16_t((r << 8) | c)) {}
+    constexpr Q_IMPLICIT QChar(short rc) noexcept : ucs(char16_t(rc)) {}
+    constexpr Q_IMPLICIT QChar(uint rc) noexcept : ucs(char16_t(rc & 0xffff)) {}
+    constexpr Q_IMPLICIT QChar(int rc) noexcept : ucs(char16_t(rc & 0xffff)) {}
+    constexpr Q_IMPLICIT QChar(SpecialCharacter s) noexcept : ucs(char16_t(s)) {} // implicit
+    constexpr Q_IMPLICIT QChar(QLatin1Char ch) noexcept : ucs(ch.unicode()) {} // implicit
+    constexpr Q_IMPLICIT QChar(char16_t ch) noexcept : ucs(ch) {} // implicit
 #if defined(Q_OS_WIN)
     static_assert(sizeof(wchar_t) == sizeof(char16_t));
 #endif
 #if defined(Q_OS_WIN) || defined(Q_CLANG_QDOC)
 #   if !defined(_WCHAR_T_DEFINED) || defined(_NATIVE_WCHAR_T_DEFINED)
-    constexpr QChar(wchar_t ch) noexcept : ucs(char16_t(ch)) {} // implicit
+    constexpr Q_IMPLICIT QChar(wchar_t ch) noexcept : ucs(char16_t(ch)) {} // implicit
 #   endif
 #endif
 
 #ifndef QT_NO_CAST_FROM_ASCII
-    QT_ASCII_CAST_WARN constexpr QChar(char c) noexcept : ucs(uchar(c)) { }
+    QT_ASCII_CAST_WARN constexpr Q_IMPLICIT QChar(char c) noexcept : ucs(uchar(c)) { }
 #ifndef QT_RESTRICTED_CAST_FROM_ASCII
-    QT_ASCII_CAST_WARN constexpr QChar(uchar c) noexcept : ucs(c) { }
+    QT_ASCII_CAST_WARN constexpr Q_IMPLICIT QChar(uchar c) noexcept : ucs(c) { }
 #endif
 #endif
 
diff --git a/src/corelib/tools/qmap.h b/src/corelib/tools/qmap.h
index 24d82fa22d..f7915b149c 100644
--- a/src/corelib/tools/qmap.h
+++ b/src/corelib/tools/qmap.h
@@ -492,7 +492,7 @@ public:
         typedef const T &reference;
 
         const_iterator() = default;
-        /* implicit */ const_iterator(const iterator &o) { i = o.i; }
+        Q_IMPLICIT const_iterator(const iterator &o) { i = o.i; }
 
         const Key &key() const { return i->first; }
         const T &value() const { return i->second; }
@@ -1116,7 +1116,7 @@ public:
         typedef const T &reference;
 
         const_iterator() = default;
-        /* implicit */ const_iterator(const iterator &o) { i = o.i; }
+        Q_IMPLICIT const_iterator(const iterator &o) { i = o.i; }
 
         const Key &key() const { return i->first; }
         const T &value() const { return i->second; }