From bf61657376c5f4827e8fe8df669d319268f51938 Mon Sep 17 00:00:00 2001
From: Mathew Sutcliffe <oktal3700@gmail.com>
Date: Sat, 2 Jul 2016 01:41:50 +0100
Subject: [PATCH] refs #698 Added equalsBy and equalsByKeys methods for
 containers.

---
 src/blackmisc/predicates.h | 29 +++++++++++++++++++++++++++++
 src/blackmisc/range.h      | 25 +++++++++++++++++++++++++
 src/blackmisc/typetraits.h | 10 ++++++++++
 3 files changed, 64 insertions(+)

diff --git a/src/blackmisc/predicates.h b/src/blackmisc/predicates.h
index 8bbc6955d..f3d21feec 100644
--- a/src/blackmisc/predicates.h
+++ b/src/blackmisc/predicates.h
@@ -72,6 +72,26 @@ namespace BlackMisc
                 template <class T> bool operator()(const T &a, const T &b) const { return head.isStable(a, b) ? head(a, b) : tail(a, b); }
             };
 
+            //! \private
+            template <class...> struct EqualsByMembers;
+
+            //! \private
+            template <class M> struct EqualsByMembers<M>
+            {
+                M m;
+                EqualsByMembers(M m_) : m(m_) {}
+                template <class T> bool operator()(const T &a, const T &b) const { return (a.*m)() == (b.*m)(); }
+            };
+
+            //! \private
+            template <class M, class... Tail> struct EqualsByMembers<M, Tail...>
+            {
+                EqualsByMembers<M> head;
+                EqualsByMembers<Tail...> tail;
+                EqualsByMembers(M m, Tail... tail_) : head(m), tail(tail_...) {}
+                template <class T> bool operator()(const T &a, const T &b) const { return head(a, b) && tail(a, b); }
+            };
+
             //! \private
             struct Matches
             {
@@ -141,6 +161,15 @@ namespace BlackMisc
             return [value = std::forward<T>(value)](const T &object) { return object == value; };
         }
 
+        /*!
+         * Returns a predicate that returns true if its arguments compare equal to each other, considering only the captured members.
+         */
+        template <class... Ts>
+        Private::EqualsByMembers<Ts...> EqualsByMembers(Ts... vs)
+        {
+            return { vs... };
+        }
+
         /*!
          * Returns a predicate that returns true if its argument matches a captured CPropertyIndexVariantMap.
          */
diff --git a/src/blackmisc/range.h b/src/blackmisc/range.h
index c4b27b905..d422d33d5 100644
--- a/src/blackmisc/range.h
+++ b/src/blackmisc/range.h
@@ -16,6 +16,7 @@
 #include "iterator.h"
 #include "predicates.h"
 #include "algorithm.h"
+#include "typetraits.h"
 #include <QtGlobal>
 #include <QDebug>
 #include <algorithm>
@@ -110,6 +111,21 @@ namespace BlackMisc
             return containsBy(BlackMisc::Predicates::MemberEqual(k0, v0, keysValues...));
         }
 
+        //! Return true if this container equals another container according to the given element equality predicate.
+        template <class T, class Predicate>
+        bool equalsBy(const T &other, Predicate c) const
+        {
+            if (equalPointers(&derived(), &other)) { return true; }
+            return std::equal(derived().begin(), derived().end(), other.begin(), other.end(), c);
+        }
+
+        //! Return true if this container equals another container, considering only the given element members.
+        template <class T, class Key0, class... Keys>
+        bool equalsByKeys(const T &other, Key0 k0, Keys... keys) const
+        {
+            return equalsBy(other, BlackMisc::Predicates::EqualsByMembers(k0, keys...));
+        }
+
         //! Copy n elements from the container at random.
         Derived randomElements(int n) const
         {
@@ -126,6 +142,15 @@ namespace BlackMisc
             return result;
         }
 
+    protected:
+        //! Efficiently compare addresses of two objects. Return false if types are not compatible.
+        //! @{
+        template <typename T, typename U, std::enable_if_t<IsEqualityComparable<const T *, const U *>::value, int> = 0>
+        static bool equalPointers(const T *a, const U *b) { return a == b; }
+        template <typename T, typename U, std::enable_if_t<! IsEqualityComparable<const T *, const U *>::value, int> = 0>
+        static bool equalPointers(const T *, const U *) { return false; }
+        //! @}
+
     private:
         Derived &derived() { return static_cast<Derived &>(*this); }
         const Derived &derived() const { return static_cast<const Derived &>(*this); }
diff --git a/src/blackmisc/typetraits.h b/src/blackmisc/typetraits.h
index 4c3f1b6e7..44f3d3d4d 100644
--- a/src/blackmisc/typetraits.h
+++ b/src/blackmisc/typetraits.h
@@ -102,6 +102,16 @@ namespace BlackMisc
     struct HasCompare<T, U, void_t<decltype(compare(std::declval<T>(), std::declval<U>()))>> : public std::true_type {};
     //! \endcond
 
+    /*!
+     * Trait which is true if the expression a == b is valid when a and b are instances of T and U.
+     */
+    template <typename T, typename U, typename = void_t<>>
+    struct IsEqualityComparable : public std::false_type {};
+    //! \cond
+    template <typename T, typename U>
+    struct IsEqualityComparable<T, U, void_t<decltype(std::declval<T>() == std::declval<U>())>> : public std::true_type {};
+    //! \endcond
+
 }
 
 #endif