From 0e5d575feceea4feac4b33e85626719e14f762a1 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Thu, 24 Feb 2022 15:49:51 +0200
Subject: Add missing optional<> comparison operators

---
 libbutl/optional.hxx | 127 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)

diff --git a/libbutl/optional.hxx b/libbutl/optional.hxx
index 28aa95a..f569f8d 100644
--- a/libbutl/optional.hxx
+++ b/libbutl/optional.hxx
@@ -291,6 +291,8 @@ namespace butl
     explicit operator bool () const {return this->v_;}
   };
 
+  // optional ? optional
+  //
   template <typename T>
   inline auto
   operator== (const optional<T>& x, const optional<T>& y)
@@ -320,6 +322,131 @@ namespace butl
   {
     return y < x;
   }
+
+  // optional ? nullopt
+  // nullopt ? optional
+  //
+  template <typename T>
+  inline auto
+  operator== (const optional<T>& x, nullopt_t)
+  {
+    bool px (x);
+    return !px;
+  }
+
+  template <typename T>
+  inline auto
+  operator== (nullopt_t, const optional<T>& y)
+  {
+    bool py (y);
+    return !py;
+  }
+
+  template <typename T>
+  inline auto
+  operator!= (const optional<T>& x, nullopt_t y)
+  {
+    return !(x == y);
+  }
+
+  template <typename T>
+  inline auto
+  operator!= (nullopt_t x, const optional<T>& y)
+  {
+    return !(x == y);
+  }
+
+  template <typename T>
+  inline auto
+  operator< (const optional<T>&, nullopt_t)
+  {
+    return false;
+  }
+
+  template <typename T>
+  inline auto
+  operator< (nullopt_t, const optional<T>& y)
+  {
+    bool py (y);
+    return py;
+  }
+
+  template <typename T>
+  inline auto
+  operator> (const optional<T>& x, nullopt_t y)
+  {
+    return y < x;
+  }
+
+  template <typename T>
+  inline auto
+  operator> (nullopt_t x, const optional<T>& y)
+  {
+    return y < x;
+  }
+
+  // optional ? T
+  // T ? optional
+  //
+  template <typename T>
+  inline auto
+  operator== (const optional<T>& x, const T& y)
+  {
+    bool px (x);
+    return px && *x == y;
+  }
+
+  template <typename T>
+  inline auto
+  operator== (const T& x, const optional<T>& y)
+  {
+    bool py (y);
+    return py && x == *y;
+  }
+
+  template <typename T>
+  inline auto
+  operator!= (const optional<T>& x, const T& y)
+  {
+    return !(x == y);
+  }
+
+  template <typename T>
+  inline auto
+  operator!= (const T& x, const optional<T>& y)
+  {
+    return !(x == y);
+  }
+
+  template <typename T>
+  inline auto
+  operator< (const optional<T>& x, const T& y)
+  {
+    bool px (x);
+    return !px || *x < y;
+  }
+
+  template <typename T>
+  inline auto
+  operator< (const T& x, const optional<T>& y)
+  {
+    bool py (y);
+    return py && x < *y;
+  }
+
+  template <typename T>
+  inline auto
+  operator> (const optional<T>& x, const T& y)
+  {
+    return y < x;
+  }
+
+  template <typename T>
+  inline auto
+  operator> (const T& x, const optional<T>& y)
+  {
+    return y < x;
+  }
 }
 
 namespace std
-- 
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