From 47e147c212dd858a23beb6c86708fa1cccd90136 Mon Sep 17 00:00:00 2001
From: Boris Kolpackov <boris@codesynthesis.com>
Date: Tue, 20 Nov 2018 13:54:00 +0200
Subject: Improve optional class template implementation

---
 libbutl/optional.ixx | 102 ++++++++++++++++++++++++++++++---------------------
 libbutl/optional.mxx |   4 +-
 2 files changed, 62 insertions(+), 44 deletions(-)

diff --git a/libbutl/optional.ixx b/libbutl/optional.ixx
index 18c0b0b..ccc7852 100644
--- a/libbutl/optional.ixx
+++ b/libbutl/optional.ixx
@@ -27,14 +27,13 @@ namespace butl
     operator= (const T& v)
     {
       if (v_)
+        d_ = v;
+      else
       {
-        d_.~T ();
-        v_ = false;
+        new (&d_) T (v);
+        v_ = true;
       }
 
-      new (&d_) T (v);
-      v_ = true;
-
       return *this;
     }
 
@@ -43,14 +42,13 @@ namespace butl
     operator= (T&& v)
     {
       if (v_)
+        d_ = std::move (v);
+      else
       {
-        d_.~T ();
-        v_ = false;
+        new (&d_) T (std::move (v));
+        v_ = true;
       }
 
-      new (&d_) T (std::move (v));
-      v_ = true;
-
       return *this;
     }
 
@@ -58,16 +56,20 @@ namespace butl
     inline optional_data<T, false>& optional_data<T, false>::
     operator= (const optional_data& o)
     {
-      if (v_)
+      if (o.v_)
       {
-        d_.~T ();
-        v_ = false;
+        if (v_)
+          d_ = o.d_;
+        else
+        {
+          new (&d_) T (o.d_);
+          v_ = true;
+        }
       }
-
-      if (o.v_)
+      else if (v_)
       {
-        new (&d_) T (o.d_);
-        v_ = true;
+        d_.~T ();
+        v_ = false;
       }
 
       return *this;
@@ -77,16 +79,20 @@ namespace butl
     inline optional_data<T, false>& optional_data<T, false>::
     operator= (optional_data&& o)
     {
-      if (v_)
+      if (o.v_)
       {
-        d_.~T ();
-        v_ = false;
+        if (v_)
+          d_ = std::move (o.d_);
+        else
+        {
+          new (&d_) T (std::move (o.d_));
+          v_ = true;
+        }
       }
-
-      if (o.v_)
+      else if (v_)
       {
-        new (&d_) T (std::move (o.d_));
-        v_ = true;
+        d_.~T ();
+        v_ = false;
       }
 
       return *this;
@@ -118,10 +124,12 @@ namespace butl
     operator= (const T& v)
     {
       if (v_)
-        v_ = false;
-
-      new (&d_) T (v);
-      v_ = true;
+        d_ = v;
+      else
+      {
+        new (&d_) T (v);
+        v_ = true;
+      }
 
       return *this;
     }
@@ -131,10 +139,12 @@ namespace butl
     operator= (T&& v)
     {
       if (v_)
-        v_ = false;
-
-      new (&d_) T (std::move (v));
-      v_ = true;
+        d_ = std::move (v);
+      else
+      {
+        new (&d_) T (std::move (v));
+        v_ = true;
+      }
 
       return *this;
     }
@@ -143,14 +153,18 @@ namespace butl
     inline optional_data<T, true>& optional_data<T, true>::
     operator= (const optional_data& o)
     {
-      if (v_)
-        v_ = false;
-
       if (o.v_)
       {
-        new (&d_) T (o.d_);
-        v_ = true;
+        if (v_)
+          d_ = o.d_;
+        else
+        {
+          new (&d_) T (o.d_);
+          v_ = true;
+        }
       }
+      else if (v_)
+        v_ = false;
 
       return *this;
     }
@@ -159,14 +173,18 @@ namespace butl
     inline optional_data<T, true>& optional_data<T, true>::
     operator= (optional_data&& o)
     {
-      if (v_)
-        v_ = false;
-
       if (o.v_)
       {
-        new (&d_) T (std::move (o.d_));
-        v_ = true;
+        if (v_)
+          d_ = std::move (o.d_);
+        else
+        {
+          new (&d_) T (std::move (o.d_));
+          v_ = true;
+        }
       }
+      else if (v_)
+        v_ = false;
 
       return *this;
     }
diff --git a/libbutl/optional.mxx b/libbutl/optional.mxx
index 0f18c11..470c608 100644
--- a/libbutl/optional.mxx
+++ b/libbutl/optional.mxx
@@ -43,7 +43,7 @@ LIBBUTL_MODEXPORT namespace butl
     template <typename T>
     struct optional_data<T, false>
     {
-      struct empty {char x;}; // Note: byte size is important to GCC.
+      struct empty {char x[sizeof(T)];}; // Note: data member important to GCC.
 
       union
       {
@@ -86,7 +86,7 @@ LIBBUTL_MODEXPORT namespace butl
     template <typename T>
     struct optional_data<T, true>
     {
-      struct empty {char x;}; // Note: byte size is important to GCC.
+      struct empty {char x[sizeof(T)];}; // Note: data member important to GCC.
 
       union
       {
-- 
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