Implement deduction guides for <array>; Reviewed as https://reviews.llvm.org/D46964

llvm-svn: 332768

libcxx/include/array

@@ -72,6 +72,9 @@ struct array
     const T* data() const noexcept;
 };
 
+  template <class T, class... U>
+    array(T, U...) -> array<T, 1 + sizeof...(U)>;
+
 template <class T, size_t N>
   bool operator==(const array<T,N>& x, const array<T,N>& y);
 template <class T, size_t N>
@@ -86,7 +89,7 @@ template <class T, size_t N>
   bool operator>=(const array<T,N>& x, const array<T,N>& y);
 
 template <class T, size_t N >
-  void swap(array<T,N>& x, array<T,N>& y) noexcept(noexcept(x.swap(y)));
+  void swap(array<T,N>& x, array<T,N>& y) noexcept(noexcept(x.swap(y))); // C++17
 
 template <class T> class tuple_size;
 template <size_t I, class T> class tuple_element;
@@ -354,6 +357,14 @@ struct _LIBCPP_TEMPLATE_VIS array<_Tp, 0>
 };
 
 
+#ifndef _LIBCPP_HAS_NO_DEDUCTION_GUIDES
+template<class _Tp, class... _Args,
+         class = typename enable_if<(is_same_v<_Tp, _Args> && ...), void>::type
+         >
+array(_Tp, _Args...)
+  -> array<_Tp, 1 + sizeof...(_Args)>;
+#endif
+
 template <class _Tp, size_t _Size>
 inline _LIBCPP_INLINE_VISIBILITY
 bool

libcxx/test/std/containers/sequences/array/array.cons/deduct.fail.cpp

@@ -0,0 +1,32 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <array>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// UNSUPPORTED: libcpp-no-deduction-guides
+
+
+// template <class T, class... U>
+//   array(T, U...) -> array<T, 1 + sizeof...(U)>;
+//
+//  Requires: (is_same_v<T, U> && ...) is true. Otherwise the program is ill-formed.
+
+
+#include <array>
+#include <cassert>
+#include <cstddef>
+
+#include "test_macros.h"
+
+int main()
+{
+    {
+    std::array arr{1,2,3L}; // expected-error {{no viable constructor or deduction guide for deduction of template arguments of 'array'}}
+    }
+}

libcxx/test/std/containers/sequences/array/array.cons/deduct.pass.cpp

@@ -0,0 +1,58 @@
+//===----------------------------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is dual licensed under the MIT and the University of Illinois Open
+// Source Licenses. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+// <array>
+// UNSUPPORTED: c++98, c++03, c++11, c++14
+// UNSUPPORTED: libcpp-no-deduction-guides
+
+
+// template <class T, class... U>
+//   array(T, U...) -> array<T, 1 + sizeof...(U)>;
+//
+//  Requires: (is_same_v<T, U> && ...) is true. Otherwise the program is ill-formed.
+
+
+#include <array>
+#include <cassert>
+#include <cstddef>
+
+#include "test_macros.h"
+
+int main()
+{
+//  Test the explicit deduction guides
+    {
+    std::array arr{1,2,3};  // array(T, U...)
+    static_assert(std::is_same_v<decltype(arr), std::array<int, 3>>, "");
+    assert(arr[0] == 1);
+    assert(arr[1] == 2);
+    assert(arr[2] == 3);
+    }
+
+    {
+    const long l1 = 42;
+    std::array arr{1L, 4L, 9L, l1}; // array(T, U...)
+    static_assert(std::is_same_v<decltype(arr)::value_type, long>, "");
+    static_assert(arr.size() == 4, "");
+    assert(arr[0] == 1);
+    assert(arr[1] == 4);
+    assert(arr[2] == 9);
+    assert(arr[3] == l1);
+    }
+
+//  Test the implicit deduction guides
+  {
+  std::array<double, 2> source = {4.0, 5.0};
+  std::array arr(source);   // array(array)
+    static_assert(std::is_same_v<decltype(arr), decltype(source)>, "");
+    static_assert(std::is_same_v<decltype(arr), std::array<double, 2>>, "");
+    assert(arr[0] == 4.0);
+    assert(arr[1] == 5.0);
+  }
+}