Merge pull request #451 from andreasfertig/fixIssue425

Fixed #425: Show the correct reference type for structured bindings.

CodeGenerator.cpp

@@ -3895,7 +3895,6 @@ void CodeGenerator::InsertArg(const BindingDecl*)
 
 void StructuredBindingsCodeGenerator::InsertArg(const BindingDecl* stmt)
 {
-    // Assume that we are looking at a builtin type. We have to construct the variable declaration information.
     const auto* bindingStmt = stmt->getBinding();
 
     // In a dependent context we have no binding and with that no type. Leave this as it is, we are looking at a
@@ -3907,17 +3906,20 @@ void StructuredBindingsCodeGenerator::InsertArg(const BindingDecl* stmt)
     // Assume that we are looking at a builtin type. We have to construct the variable declaration information.
     auto type = stmt->getType();
 
-    // If we have holding var we are looking at a user defined type like tuple and those the defaults from above are
+    // If we have a holding var we are looking at a user defined type like tuple and those the defaults from above are
     // wrong. This type contains the variable declaration so we insert this.
     if(const auto* holdingVar = stmt->getHoldingVar()) {
-        // A rvalue reference boils down to just the type. If it is a reference then it is a lvalue reference at this
-        // point. Hence we need to strip the &&.
+        // Initial paper: http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2015/p0144r0.pdf
+
+        // The type of the binding depends on the initializer. In case the initializer is an lvalue we get a T&,
+        // otherwise a T&&. We typically look at an lvalue if the decomposition declaration was auto& [a,b]. Note the &
+        // here We have a rvalue in case the decomposition declaration was auto [a,b]. Note no reference. The standard
+        // std::get returns a lvalue reference in case e in get(e) is an lvalue, otherwise it returns an rvalue
+        // reference because then the call is get(std::move(e))
         type = holdingVar->getType().getCanonicalType();
-        if(type->isRValueReferenceType()) {
-            type = type.getNonReferenceType();
-        }
 
         bindingStmt = holdingVar->getAnyInitializer();
+
     } else if(not type->isLValueReferenceType()) {
         type = stmt->getASTContext().getLValueReferenceType(type);
     }

tests/Issue131.expect

@@ -4,6 +4,6 @@ std::tuple<int, float> foo();
 
 
 std::tuple<int, float> __foo5 = foo();
-int a = std::get<0UL>(static_cast<std::tuple<int, float> &&>(__foo5));
-float b = std::get<1UL>(static_cast<std::tuple<int, float> &&>(__foo5));
+int && a = std::get<0UL>(static_cast<std::tuple<int, float> &&>(__foo5));
+float && b = std::get<1UL>(static_cast<std::tuple<int, float> &&>(__foo5));
 

tests/Issue20.expect

@@ -4,8 +4,8 @@ int main()
 {
   std::map<int, int> map = std::map<int, int, std::less<int>, std::allocator<std::pair<const int, int> > >{std::initializer_list<std::pair<const int, int> >{std::pair<const int, int>{1, 2}}, std::less<int>()};
   std::pair<const int, int> __operator6 = std::pair<const int, int>(map.begin().operator*());
-  const int key = std::get<0UL>(static_cast<std::pair<const int, int> &&>(__operator6));
-  int value = std::get<1UL>(static_cast<std::pair<const int, int> &&>(__operator6));
+  const int && key = std::get<0UL>(static_cast<std::pair<const int, int> &&>(__operator6));
+  int && value = std::get<1UL>(static_cast<std::pair<const int, int> &&>(__operator6));
   return 0;
 }
 

tests/Issue381.expect

@@ -4,8 +4,8 @@ int main()
 {
   std::tuple<int, int> tup = std::tuple<int, int>{2, 5};
   std::tuple<int, int> __tup6 = std::tuple<int, int>(tup);
-  int a = std::get<0UL>(static_cast<std::tuple<int, int> &&>(__tup6));
-  int b = std::get<1UL>(static_cast<std::tuple<int, int> &&>(__tup6));
+  int && a = std::get<0UL>(static_cast<std::tuple<int, int> &&>(__tup6));
+  int && b = std::get<1UL>(static_cast<std::tuple<int, int> &&>(__tup6));
   return 0;
 }
 

tests/Issue425.cpp

@@ -0,0 +1,7 @@
+#include <utility>
+
+int main()
+{
+    std::pair<int, char> p;
+  	auto [a, b] = p;
+}

tests/Issue425.expect

@@ -0,0 +1,11 @@
+#include <utility>
+
+int main()
+{
+  std::pair<int, char> p = std::pair<int, char>();
+  std::pair<int, char> __p6 = std::pair<int, char>(p);
+  int && a = std::get<0UL>(static_cast<std::pair<int, char> &&>(__p6));
+  char && b = std::get<1UL>(static_cast<std::pair<int, char> &&>(__p6));
+  return 0;
+}
+

tests/StructuredBindingsHandler10Test.cpp

@@ -0,0 +1,12 @@
+// Source: https://en.cppreference.com/w/cpp/language/structured_binding
+#include <tuple>
+
+float x{};
+char  y{};
+int   z{};
+
+std::tuple<float&,char&&,int> tpl(x,std::move(y),z);
+const auto& [a,b,c] = tpl;
+// a names a structured binding that refers to x; decltype(a) is float&
+// b names a structured binding that refers to y; decltype(b) is char&&
+// c names a structured binding that refers to the 3rd element of tpl; decltype(c) is const int

tests/StructuredBindingsHandler10Test.expect

@@ -0,0 +1,20 @@
+// Source: https://en.cppreference.com/w/cpp/language/structured_binding
+#include <tuple>
+
+float x = {};
+
+char y = {};
+
+int z = {};
+
+
+std::tuple<float &, char &&, int> tpl = std::tuple<float &, char &&, int>(x, std::move(y), z);
+
+const std::tuple<float &, char &&, int> & __tpl9 = tpl;
+float & a = std::get<0UL>(__tpl9);
+char & b = std::get<1UL>(__tpl9);
+const int & c = std::get<2UL>(__tpl9);
+
+// a names a structured binding that refers to x; decltype(a) is float&
+// b names a structured binding that refers to y; decltype(b) is char&&
+// c names a structured binding that refers to the 3rd element of tpl; decltype(c) is const int

tests/StructuredBindingsHandler3Test.expect

@@ -105,25 +105,25 @@ namespace constant
 {
   Q q = Q();
   Q __q17 = Q(q);
-  int a = get<0UL>(static_cast<Q &&>(__q17));
-  int b = get<1UL>(static_cast<Q &&>(__q17));
-  int c = get<2UL>(static_cast<Q &&>(__q17));
+  int && a = get<0UL>(static_cast<Q &&>(__q17));
+  int && b = get<1UL>(static_cast<Q &&>(__q17));
+  int && c = get<2UL>(static_cast<Q &&>(__q17));
   inline constexpr bool f()
   {
     Q __q19 = Q(q);
-    int a = get<0UL>(static_cast<Q &&>(__q19));
-    int b = get<1UL>(static_cast<Q &&>(__q19));
-    int c = get<2UL>(static_cast<Q &&>(__q19));
+    int && a = get<0UL>(static_cast<Q &&>(__q19));
+    int && b = get<1UL>(static_cast<Q &&>(__q19));
+    int && c = get<2UL>(static_cast<Q &&>(__q19));
     return ((a == 0) && (b == 1)) && (c == 4);
   }
   inline constexpr int g()
   {
     int * p = nullptr;
     {
       Q __q26 = Q(q);
-      int a = get<0UL>(static_cast<Q &&>(__q26));
-      int b = get<1UL>(static_cast<Q &&>(__q26));
-      int c = get<2UL>(static_cast<Q &&>(__q26));
+      int && a = get<0UL>(static_cast<Q &&>(__q26));
+      int && b = get<1UL>(static_cast<Q &&>(__q26));
+      int && c = get<2UL>(static_cast<Q &&>(__q26));
       p = &c;
     };
     return *p;

tests/StructuredBindingsHandler5Test.expect

@@ -152,7 +152,7 @@ int main()
   Point p = Point{1, 2};
   Point & __p64 = p;
   double & x = __p64.get<0>();
-  double y = __p64.get<1>();
+  double && y = __p64.get<1>();
   printf("x:%lf y:%lf\n", p.GetX(), p.GetY());
   ++x;
   ++y;
@@ -161,7 +161,7 @@ int main()
   constexpr const Point p2 = Point{3, 4};
   const Point & __p273 = p2;
   const double & x2 = __p273.get<0>();
-  const double y2 = static_cast<const double>(__p273.get<1>());
+  const double && y2 = static_cast<const double>(__p273.get<1>());
   return 0;
 }
 

tests/StructuredBindingsHandler6Test.expect

@@ -115,8 +115,8 @@ int main()
 {
   Point p = Point{1, 2};
   Point __p58 = Point(p);
-  double x = static_cast<const Point &&>(__p58).get<0>();
-  double y = static_cast<const Point &&>(__p58).get<1>();
+  double && x = static_cast<const Point &&>(__p58).get<0>();
+  double && y = static_cast<const Point &&>(__p58).get<1>();
   printf("x:%lf y:%lf\n", p.GetX(), p.GetY());
   printf("x:%lf y:%lf\n", x, y);
   char ar[2] = {7, 8};
@@ -143,9 +143,9 @@ int main()
   char & c = std::get<1UL>(__muple80);
   double & d = std::get<2UL>(__muple80);
   std::tuple<int, char, double> __muple82 = std::tuple<int, char, double>(muple);
-  int ii = std::get<0UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
-  char cc = std::get<1UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
-  double dd = std::get<2UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
+  int && ii = std::get<0UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
+  char && cc = std::get<1UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
+  double && dd = std::get<2UL>(static_cast<std::tuple<int, char, double> &&>(__muple82));
   return 0;
 }
 

tests/StructuredBindingsHandler8Test.cpp

@@ -0,0 +1,10 @@
+#include <tuple>
+
+auto tup = std::tuple<int, int>{2, 5};
+auto [a1, b1] = tup;
+
+
+int i = 5;
+auto tup2 = std::tuple<int, int&>{2, i};
+auto [a2, b2] = tup2;
+

tests/StructuredBindingsHandler8Test.expect

@@ -0,0 +1,19 @@
+#include <tuple>
+
+std::tuple<int, int> tup = std::tuple<int, int>{2, 5};
+
+std::tuple<int, int> __tup4 = std::tuple<int, int>(tup);
+int && a1 = std::get<0UL>(static_cast<std::tuple<int, int> &&>(__tup4));
+int && b1 = std::get<1UL>(static_cast<std::tuple<int, int> &&>(__tup4));
+
+
+
+int i = 5;
+
+std::tuple<int, int &> tup2 = std::tuple<int, int &>{2, i};
+
+std::tuple<int, int &> __tup29 = std::tuple<int, int &>(tup2);
+int && a2 = std::get<0UL>(static_cast<std::tuple<int, int &> &&>(__tup29));
+int & b2 = std::get<1UL>(static_cast<std::tuple<int, int &> &&>(__tup29));
+
+

tests/StructuredBindingsHandler9Test.expect

@@ -4,8 +4,8 @@ std::tuple<int, float> foo = std::tuple<int, float>();
 
 
 std::tuple<int, float> __foo5 = std::tuple<int, float>(foo);
-int a = std::get<0UL>(static_cast<std::tuple<int, float> &&>(__foo5));
-float b = std::get<1UL>(static_cast<std::tuple<int, float> &&>(__foo5));
+int && a = std::get<0UL>(static_cast<std::tuple<int, float> &&>(__foo5));
+float && b = std::get<1UL>(static_cast<std::tuple<int, float> &&>(__foo5));
 
 std::tuple<int, float> & __foo6 = foo;
 int & ra = std::get<0UL>(__foo6);

tests/TupeInRangeBasedForTest.expect

@@ -28,8 +28,8 @@ int main()
     std::__wrap_iter<std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> *> __end1 = __range1.end();
     for(; std::operator!=(__begin1, __end1); __begin1.operator++()) {
       std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> __operator15 = std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int>(__begin1.operator*());
-      std::basic_string<char, std::char_traits<char>, std::allocator<char> > s = std::get<0UL>(static_cast<std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> &&>(__operator15));
-      int n = std::get<1UL>(static_cast<std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> &&>(__operator15));
+      std::basic_string<char, std::char_traits<char>, std::allocator<char> > && s = std::get<0UL>(static_cast<std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> &&>(__operator15));
+      int && n = std::get<1UL>(static_cast<std::tuple<std::basic_string<char, std::char_traits<char>, std::allocator<char> >, int> &&>(__operator15));
       printf("c=%s, n=%d\n", s.c_str(), n);
     }
 

tests/dcl.struct.bind.Test.cpp

@@ -0,0 +1,86 @@
+
+// p1
+// cv := denote the cv-qualifiers in the decl-specifier-seq
+// S  := consist of the storage-class-specifiers of the decl-specifier-seq (if any)
+//
+// 1) a variable with a unique name e is introduced. 
+//    If the assignment-expression in the initializer has array type A and no ref-qualifier is present, e is defined by:
+// 
+//    attribute-specifier-seq_{opt} S cv A e ;
+//
+//    otherwise e is defined as-if by:
+//
+//   attribute-specifier-seq_{opt} decl-specifier-seq ref-qualifier_{opt} e initializer ;
+//
+//   The type of the id-expression e is called E.
+//
+//   Note: E is never a reference type
+//
+//
+// -- tuple --
+// Let i be an index of type std::size_t corresponding to vi
+// either:
+//  e.get<i>()
+//  get<i>(e)
+//
+//  In either case, 
+//      - e is an lvalue if the type of the entity e is an lvalue reference and 
+//      - an xvalue otherwise. 
+//
+//  -> auto& [a ,b ] -> e := lvalue
+//  -> auto  [a ,b ] -> e := xvalue
+//
+//  T_i  := std::tuple_element<i, E>::type 
+//  U_i  := either
+//           - T_i&:  if the initializer is an lvalue,
+//           - T_i&&: an rvalue reference otherwise, 
+//
+//  variables are introduced with unique names r_i as follows:
+//
+//      S U_i r_i = initializer ;
+//
+//  Each vi is the name of an lvalue of type Ti that refers to the object bound to ri; the referenced type is Ti.
+//
+
+
+// The lvalue is a bit-field if that member is a bit-field. [Example:
+//      struct S { int x1 : 2; volatile double y1; };
+//      S f();
+//      const auto [ x, y ] = f();
+// The type of the id-expression x is “const int”, the type of the id-expression y is “const volatile double”. —end example]
+
+
+// For each identifier, a variable whose type is "reference to std::tuple_element<i, E>::type" is introduced: lvalue reference if its corresponding initializer is an lvalue, rvalue reference otherwise. The initializer for the i-th variable is
+// - e.get<i>(), if lookup for the identifier get in the scope of E by class member access lookup finds at least one declaration that is a function template whose first template parameter is a non-type parameter
+// - Otherwise, get<i>(e), where get is looked up by argument-dependent lookup only, ignoring non-ADL lookup. 
+// 
+// The initializer for the new variable is e.get<i> or get<i>(e). 
+// Here the overload of get that is called is a rvalue in case we use auto and an lvalue in case we use auto&
+
+
+
+#include <cassert>
+#include <tuple>
+
+// https://en.cppreference.com/w/cpp/language/structured_binding
+float x{};
+char  y{};
+int   z{};
+
+std::tuple<float&,char&&,int> tpl(x,std::move(y),z);
+//auto tpl = std::tuple{x,std::move(y),z};
+auto& [a,b,c] = tpl;
+// a names a structured binding that refers to x; decltype(a) is float&
+// b names a structured binding that refers to y; decltype(b) is char&&
+// c names a structured binding that refers to the 3rd element of tpl; decltype(c) is int
+
+int main() {
+    a = 4.5;
+    c = 5;
+
+//    assert(4.5 == x);
+//    assert(0 == z);
+
+//    std::cout << a << '\n';
+//    std::cout << z << '\n';
+}