From ee2e33507221ee3ab4a1be43442844461b892b3d Mon Sep 17 00:00:00 2001
From: Jan Travnicek <Jan.Travnicek@fit.cvut.cz>
Date: Fri, 10 Apr 2020 07:45:15 +0200
Subject: [PATCH] do not copy the variant in its visitor
---
alib2std/src/extensions/container/variant.hpp | 35 ++++----
.../extensions/container/VariantTest.cpp | 82 +++++++++++++++++++
2 files changed, 101 insertions(+), 16 deletions(-)
diff --git a/alib2std/src/extensions/container/variant.hpp b/alib2std/src/extensions/container/variant.hpp
index c01ddbe70a..8c8194e7f3 100644
--- a/alib2std/src/extensions/container/variant.hpp
+++ b/alib2std/src/extensions/container/variant.hpp
@@ -40,21 +40,7 @@ namespace ext {
template < class Visitor, class... Variants >
constexpr auto visit ( Visitor && vis, Variants && ... vars ) {
- auto extToStd = [] ( auto && variant ) {
- using __std__variant = typename std::decay_t < decltype ( variant ) >::__base;
-
- if constexpr ( std::is_lvalue_reference_v < decltype ( variant ) > && std::is_const_v < std::remove_reference_t < decltype ( variant ) > > ) {
- return static_cast < const __std__variant & > ( variant );
- } else if constexpr ( std::is_lvalue_reference_v < decltype ( variant ) > ) {
- return static_cast < __std__variant & > ( variant );
- } else if constexpr ( std::is_rvalue_reference_v < decltype ( variant ) > ) {
- return static_cast < __std__variant && > ( variant );
- } else {
- static_assert ( "Unhandled option" );
- }
- };
-
- return std::visit ( std::forward < Visitor > ( vis ), extToStd ( std::forward < Variants > ( vars ) ) ... );
+ return std::visit ( std::forward < Visitor > ( vis ), std::forward < Variants > ( vars ).asStdVariant ( ) ... );
}
/**
@@ -107,6 +93,10 @@ using __std__variant = typename variant_builder_start < Ts ... >::__std__variant
*/
template < typename ... Ts >
class variant : public __std__variant < Ts ... > {
+
+ template < class Visitor, class... Variants >
+ friend constexpr auto visit ( Visitor && vis, Variants && ... vars );
+
/**
* Internal variant to string callback implementation.
*/
@@ -178,12 +168,25 @@ class variant : public __std__variant < Ts ... > {
return - second.compare ( first );
}
};
-public:
+
/**
* Remember the base class, i.e. std::variant
*/
typedef __std__variant < Ts ... > __base;
+ const __base & asStdVariant ( ) const & {
+ return * this;
+ }
+
+ __base & asStdVariant ( ) & {
+ return * this;
+ }
+
+ __base && asStdVariant ( ) && {
+ return std::move ( * this );
+ }
+
+public:
/**
* Inherit constructors of the standard variant
*/
diff --git a/alib2std/test-src/extensions/container/VariantTest.cpp b/alib2std/test-src/extensions/container/VariantTest.cpp
index 4294e1edf7..3d44695bc9 100644
--- a/alib2std/test-src/extensions/container/VariantTest.cpp
+++ b/alib2std/test-src/extensions/container/VariantTest.cpp
@@ -68,6 +68,51 @@ namespace {
test2(int i) : m_i(i) {}
};
+
+ class Moveable {
+ int& m_moves;
+ int& m_copies;
+
+ public:
+ Moveable(int& moves, int& copies) : m_moves(moves), m_copies(copies) {
+ m_moves = 0;
+ m_copies = 0;
+ }
+
+ Moveable(const Moveable& src) : m_moves(src.m_moves), m_copies(src.m_copies) {
+ m_copies++;
+ }
+
+ Moveable(Moveable&& src) : m_moves(src.m_moves), m_copies(src.m_copies) {
+ m_moves++;
+ }
+
+ Moveable & operator = ( const Moveable & ) {
+ m_copies ++;
+ return * this;
+ }
+
+ Moveable & operator = ( Moveable && ) {
+ m_moves ++;
+ return * this;
+ }
+
+ bool operator<(const Moveable&) const {
+ return false;
+ }
+
+ bool operator==(const Moveable&) const {
+ return true;
+ }
+
+ bool operator!=(const Moveable&) const {
+ return false;
+ }
+
+ friend std::ostream & operator << ( std::ostream & os, const Moveable & ) {
+ return os << "Moveable";
+ }
+ };
}
namespace ext {
@@ -79,6 +124,13 @@ namespace ext {
}
};
+ template<>
+ struct compare<Moveable> {
+ int operator()(const Moveable& , const Moveable& ) {
+ return 0;
+ }
+ };
+
} /* namespace ext */
TEST_CASE ( "Variant", "[unit][std][container]" ) {
@@ -232,4 +284,34 @@ TEST_CASE ( "Variant", "[unit][std][container]" ) {
v = std::move ( v2 );
v.get < std::set < int > > ( ).insert ( 1 );
}
+
+ SECTION ( "Copy vs. Move" ) {
+ int moves = 0;
+ int copies = 0;
+
+ ext::variant < Moveable, int > inst1 ( Moveable ( moves, copies ) );
+
+ CHECK ( moves == 1 );
+ CHECK ( copies == 0 );
+
+ ext::variant < Moveable, int > inst2 ( 1 );
+
+ CHECK ( moves == 1 );
+ CHECK ( copies == 0 );
+
+ CHECK ( inst1 != inst2 );
+
+ CHECK ( moves == 1 );
+ CHECK ( copies == 0 );
+
+ std::cout << inst1 << std::endl;
+
+ CHECK ( moves == 1 );
+ CHECK ( copies == 0 );
+
+ inst1.compare ( inst2 );
+
+ CHECK ( moves == 1 );
+ CHECK ( copies == 0 );
+ }
}
--
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