From d489bed3705b78e99201e9e336952c2bca923d81 Mon Sep 17 00:00:00 2001
From: Klaus Basan <klaus.basan@klausbasan.de>
Date: Mon, 9 Jul 2018 22:06:03 +0200
Subject: [PATCH] Ref T268, compare for PQs

---
 src/blackmisc/pq/physicalquantity.cpp |  9 +++++++--
 src/blackmisc/pq/physicalquantity.h   | 10 ++++++++--
 2 files changed, 15 insertions(+), 4 deletions(-)

diff --git a/src/blackmisc/pq/physicalquantity.cpp b/src/blackmisc/pq/physicalquantity.cpp
index ea993ef2f..8737a92e0 100644
--- a/src/blackmisc/pq/physicalquantity.cpp
+++ b/src/blackmisc/pq/physicalquantity.cpp
@@ -500,8 +500,13 @@ namespace BlackMisc
         template <class MU, class PQ>
         int CPhysicalQuantity<MU, PQ>::compareImpl(const PQ &a, const PQ &b)
         {
-            if (a.isNull() > b.isNull()) { return -1; }
-            if (a.isNull() < b.isNull()) { return 1; }
+            // fetch "null" as we do not know how expensive it is
+            const bool aIsNull = a.isNull();
+            const bool bIsNull = b.isNull();
+
+            if (aIsNull && bIsNull) { return 0; }
+            if (aIsNull > bIsNull)  { return -1; }
+            if (aIsNull < bIsNull)  { return 1; }
 
             if (a < b) { return -1; }
             else if (a > b) { return 1; }
diff --git a/src/blackmisc/pq/physicalquantity.h b/src/blackmisc/pq/physicalquantity.h
index 7d914002a..e501d30fc 100644
--- a/src/blackmisc/pq/physicalquantity.h
+++ b/src/blackmisc/pq/physicalquantity.h
@@ -228,6 +228,9 @@ namespace BlackMisc
             //! \copydoc BlackMisc::Mixin::Index::setPropertyByIndex
             void setPropertyByIndex(const CPropertyIndex &index, const CVariant &variant);
 
+            //! \copydoc BlackMisc::Mixin::Index::comparePropertyByIndex
+            int comparePropertyByIndex(const CPropertyIndex &index, const PQ &pq) const;
+
             //! \copydoc BlackMisc::Mixin::String::toQString
             QString convertToQString(bool i18n = false) const;
 
@@ -237,8 +240,8 @@ namespace BlackMisc
             //! Parse value from string
             void parseFromString(const QString &value);
 
-            //! Compare
-            int comparePropertyByIndex(const CPropertyIndex &index, const PQ &pq) const;
+            //! Compare with other PQ
+            int compare(const PQ &other) const { return compareImpl(*this->derived(), other); }
 
             //! Maximum of 2 quantities
             static const PQ &maxValue(const PQ &pq1, const PQ &pq2);
@@ -246,6 +249,9 @@ namespace BlackMisc
             //! Minimum of 2 quantities
             static const PQ &minValue(const PQ &pq1, const PQ &pq2);
 
+            //! Implementation of compare
+            static int compare(const PQ &a, const PQ &b) { return compareImpl(a, b); }
+
             //! NULL PQ
             static const PQ &null();