From 3ef8ec2ee187b949b3f6840ca03bcc0e814c00a9 Mon Sep 17 00:00:00 2001
From: Lars Knoll <lars.knoll@qt.io>
Date: Mon, 6 Jul 2020 14:06:08 +0200
Subject: Constrain the data stream operators for containers

Check that we can successfully instantiate the data
stream operator for a container before we actually try.

This is required so we can automate registration of debug
stream operators with QMetaType.

Change-Id: Ib100a5242470d7fc8067058cc4d81af2fa9354b0
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
---
 src/corelib/global/qtypeinfo.h | 11 +++++++++++
 1 file changed, 11 insertions(+)

(limited to 'src/corelib/global')

diff --git a/src/corelib/global/qtypeinfo.h b/src/corelib/global/qtypeinfo.h
index 2f7bb414b5..e45347ee10 100644
--- a/src/corelib/global/qtypeinfo.h
+++ b/src/corelib/global/qtypeinfo.h
@@ -464,6 +464,17 @@ struct has_ostream_operator<Stream, T, std::void_t<decltype(detail::reference<St
 template <typename Stream, typename T>
 constexpr bool has_ostream_operator_v = has_ostream_operator<Stream, T>::value;
 
+template <typename Stream, typename, typename = void>
+struct has_istream_operator : std::false_type {};
+template <typename Stream, typename T>
+struct has_istream_operator<Stream, T, std::void_t<decltype(detail::reference<Stream>() >> detail::reference<T>())>>
+        : std::true_type {};
+template <typename Stream, typename T>
+constexpr bool has_istream_operator_v = has_istream_operator<Stream, T>::value;
+
+template <typename Stream, typename T>
+constexpr bool has_stream_operator_v = has_ostream_operator_v<Stream, T> && has_istream_operator_v<Stream, T>;
+
 }
 
 
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