Update documentation

.drone.jsonnet

@@ -235,6 +235,76 @@ local windows_pipeline(name, image, environment, arch = "amd64") =
         "clang-3.8",
     ),
 
+    linux_pipeline(
+        "Linux 18.04 Clang 3.9",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-3.9', CXXSTD: '03,11,14' },
+        "clang-3.9",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 4.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-4.0', CXXSTD: '03,11,14' },
+        "clang-4.0",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 5.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-5.0', CXXSTD: '03,11,14,1z' },
+        "clang-5.0",
+    ),
+
+    linux_pipeline(
+        "Linux 18.04 Clang 6.0",
+        "cppalliance/droneubuntu1804:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-6.0', CXXSTD: '03,11,14,17' },
+        "clang-6.0",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 7",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-7', CXXSTD: '03,11,14,17' },
+        "clang-7",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 8",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-8', CXXSTD: '03,11,14,17' },
+        "clang-8",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 9",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-9', CXXSTD: '03,11,14,17,2a' },
+        "clang-9",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 10",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-10', CXXSTD: '03,11,14,17,2a' },
+        "clang-10",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 11",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-11', CXXSTD: '03,11,14,17,2a' },
+        "clang-11",
+    ),
+
+    linux_pipeline(
+        "Linux 20.04 Clang 12",
+        "cppalliance/droneubuntu2004:1",
+        { TOOLSET: 'clang', COMPILER: 'clang++-12', CXXSTD: '03,11,14,17,2a' },
+        "clang-12",
+    ),
+
     linux_pipeline(
         "Linux 22.04 Clang 13",
         "cppalliance/droneubuntu2204:1",

CMakeLists.txt

@@ -16,7 +16,6 @@ target_link_libraries(boost_array
   INTERFACE
     Boost::assert
     Boost::config
-    Boost::core
     Boost::static_assert
     Boost::throw_exception
 )

build.jam

@@ -0,0 +1,24 @@
+# Copyright 2023-2024 René Ferdinand Rivera Morell
+# Copyright 2024 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# https://www.boost.org/LICENSE_1_0.txt
+
+require-b2 5.2 ;
+
+constant boost_dependencies :
+    /boost/assert//boost_assert
+    /boost/config//boost_config
+    /boost/static_assert//boost_static_assert
+    /boost/throw_exception//boost_throw_exception
+    ;
+
+project /boost/array ;
+
+explicit
+    [ alias boost_array : : : : <include>include <library>$(boost_dependencies) ]
+    [ alias all : boost_array test ]
+    ;
+
+call-if : boost-library array
+    ;
+

doc/array/changes.adoc

@@ -14,3 +14,11 @@ http://www.boost.org/LICENSE_1_0.txt
 
 * Converted documentation to AsciiDoc (Christian Mazakas).
 * Added `noexcept` and `constexpr` as appropriate.
+* Marked obsolete functions as deprecated.
+* Removed obsolete compiler workarounds.
+* Changed `array<T, 0>::begin()`, `cbegin()`, `end()`, `cend()` to return `nullptr`, enabling `constexpr`.
+  This matches the behavior of `std::array`.
+* Removed local `hash_value` overload; `boost::hash` supports array-like types natively.
+* `array<T, 0>` can now be initialized with `= {{}}`.
+* Added `operator\<\=>`.
+* Added `to_array`.

doc/array/reference.adoc

@@ -35,10 +35,20 @@ namespace boost {
   template<typename T, std::size_t N>
     constexpr bool operator>=(const array<T, N>&, const array<T, N>&);
 
+  template<typename T, std::size_t N>
+    constexpr auto operator<=>(const array<T, N>&, const array<T, N>&);
+
   template<std::size_t Idx, typename T, std::size_t N>
     constexpr T& get(array<T, N>&) noexcept;
   template<std::size_t Idx, typename T, std::size_t N>
     constexpr const T& get(const array<T, N>&) noexcept;
+
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T const (&)[N] );
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T (&&)[N] );
+  template<class T, std::size_t N>
+    constexpr array<T, N> to_array( T const (&&)[N] );
 }
 ```
 
@@ -136,7 +146,7 @@ public:
 template<typename U> array& operator=(const array<U, N>& other);
 ```
 [horizontal]
-Effects: :: `std::copy(rhs.begin(), rhs.end(), begin())`.
+Effects: :: For each `i` in `[0..N)`, performs `elems[i] = other.elems[i];`.
 
 ---
 
@@ -233,7 +243,7 @@ constexpr const_reference operator[](size_type i) const;
 [horizontal]
 Requires: :: `i < N`.
 Returns: ::  `elems[i]`.
-Throws: :: nothing.
+Throws: :: Nothing.
 
 ---
 
@@ -254,7 +264,7 @@ constexpr const_reference front() const;
 [horizontal]
 Requires: ::  `N > 0`.
 Returns: :: `elems[0]`.
-Throws: :: nothing.
+Throws: :: Nothing.
 
 ---
 
@@ -265,7 +275,7 @@ constexpr const_reference back() const;
 [horizontal]
 Requires: :: `N > 0`.
 Returns: :: `elems[N-1]`.
-Throws: :: nothing.
+Throws: :: Nothing.
 
 ---
 
@@ -302,7 +312,7 @@ Complexity: :: linear in `N`.
 void fill(const T& value);
 ```
 [horizontal]
-Effects: :: for each `i` in `[0..N)`, performs `elems[i] = value;`.
+Effects: :: For each `i` in `[0..N)`, performs `elems[i] = value;`.
 
 ---
 
@@ -382,6 +392,17 @@ Returns: :: `!(x < y)`.
 
 ---
 
+```
+template<typename T, std::size_t N>
+  constexpr auto operator<=>(const array<T, N>& x, const array<T, N>& y)
+  -> decltype(x[0] <=> y[0]);
+```
+[horizontal]
+Effects: :: For each `i` in `[0..N)`, if `(x[i] \<\=> y[i]) != 0`, returns `x[i] \<\=> y[i]`. Otherwise, returns `std::strong_ordering::equal`, converted to the return type.
+Remarks: :: When `N` is 0, the return type is `std::strong_ordering` and the return value is `std::strong_ordering::equal`.
+
+---
+
 ### Specializations
 
 ```
@@ -403,3 +424,29 @@ Mandates: :: `Idx < N`.
 Returns: :: `arr[Idx]`.
 
 ---
+
+
+### Creation
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T const (&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is copied from `a[i]`.
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T (&&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is moved from `std::move(a[i])`.
+
+```
+template<class T, std::size_t N>
+  constexpr array<T, N> to_array( T const (&&a)[N] );
+```
+[horizontal]
+Returns: :: an `array<T, N>` `r` such that for each `i` in `[0..N)`, `r[i]` is copied from `a[i]`.
+
+---

include/boost/array.hpp

@@ -37,9 +37,10 @@
 
 #if BOOST_WORKAROUND(BOOST_MSVC, >= 1400)
 # pragma warning(push)
-# pragma warning(disable:4510) // boost::array<T,N>' : default constructor could not be generated
-# pragma warning(disable:4512) // boost::array<T,N>' : assignment operator could not be generated
-# pragma warning(disable:4610) // class 'boost::array<T,N>' can never be instantiated - user defined constructor required
+# pragma warning(disable: 4510) // boost::array<T,N>' : default constructor could not be generated
+# pragma warning(disable: 4512) // boost::array<T,N>' : assignment operator could not be generated
+# pragma warning(disable: 4610) // class 'boost::array<T,N>' can never be instantiated - user defined constructor required
+# pragma warning(disable: 4702) // unreachable code
 #endif
 
 #include <boost/assert.hpp>
@@ -50,6 +51,12 @@
 #include <utility>
 #include <cstddef>
 
+#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
+# if __has_include(<compare>)
+#  include <compare>
+# endif
+#endif
+
 namespace boost {
 
     template<class T, std::size_t N>
@@ -195,6 +202,8 @@ namespace boost {
 
     template< class T >
     class array< T, 0 > {
+      public:
+        struct {} elems; // enables initialization with = {{}}
 
       public:
         // type definitions
@@ -207,13 +216,13 @@ namespace boost {
         typedef std::ptrdiff_t difference_type;
 
         // iterator support
-        iterator        begin()       BOOST_NOEXCEPT { return       iterator( reinterpret_cast<       T * >( this ) ); }
-        const_iterator  begin() const BOOST_NOEXCEPT { return const_iterator( reinterpret_cast< const T * >( this ) ); }
-        const_iterator cbegin() const BOOST_NOEXCEPT { return const_iterator( reinterpret_cast< const T * >( this ) ); }
+        BOOST_CXX14_CONSTEXPR iterator  begin()       BOOST_NOEXCEPT { return data(); }
+        BOOST_CONSTEXPR const_iterator  begin() const BOOST_NOEXCEPT { return data(); }
+        BOOST_CONSTEXPR const_iterator cbegin() const BOOST_NOEXCEPT { return data(); }
 
-        iterator        end()       BOOST_NOEXCEPT { return  begin(); }
-        const_iterator  end() const BOOST_NOEXCEPT { return  begin(); }
-        const_iterator cend() const BOOST_NOEXCEPT { return cbegin(); }
+        BOOST_CXX14_CONSTEXPR iterator  end()       BOOST_NOEXCEPT { return  begin(); }
+        BOOST_CONSTEXPR const_iterator  end() const BOOST_NOEXCEPT { return  begin(); }
+        BOOST_CONSTEXPR const_iterator cend() const BOOST_NOEXCEPT { return cbegin(); }
 
         // reverse iterator support
         typedef std::reverse_iterator<iterator> reverse_iterator;
@@ -303,19 +312,10 @@ namespace boost {
         BOOST_CXX14_CONSTEXPR void fill (const T& ) {}
 
         // check range (may be private because it is static)
-        static reference failed_rangecheck () {
-                std::out_of_range e("attempt to access element of an empty array");
-                boost::throw_exception(e);
-#if defined(BOOST_NO_EXCEPTIONS) || (!defined(BOOST_MSVC) && !defined(__PATHSCALE__))
-                //
-                // We need to return something here to keep
-                // some compilers happy: however we will never
-                // actually get here....
-                //
-                static T placeholder;
-                return placeholder;
-#endif
-            }
+        static reference failed_rangecheck ()
+        {
+            boost::throw_exception( std::out_of_range( "attempt to access element of an empty array" ) );
+        }
     };
 
     // comparisons
@@ -333,7 +333,7 @@ namespace boost {
 #if BOOST_WORKAROUND(BOOST_GCC, < 90000)
 
     template<class T>
-    BOOST_CXX14_CONSTEXPR bool operator== (const array<T, 0>& x, const array<T, 0>& y)
+    BOOST_CXX14_CONSTEXPR bool operator== (const array<T, 0>& /*x*/, const array<T, 0>& /*y*/)
     {
         return true;
     }
@@ -360,7 +360,7 @@ namespace boost {
 #if BOOST_WORKAROUND(BOOST_GCC, < 90000)
 
     template<class T>
-    BOOST_CXX14_CONSTEXPR bool operator< (const array<T, 0>& x, const array<T, 0>& y)
+    BOOST_CXX14_CONSTEXPR bool operator< (const array<T, 0>& /*x*/, const array<T, 0>& /*y*/)
     {
         return false;
     }
@@ -388,6 +388,32 @@ namespace boost {
         x.swap(y);
     }
 
+#if defined(__cpp_impl_three_way_comparison) && __cpp_impl_three_way_comparison >= 201907L
+# if __has_include(<compare>)
+
+    template<class T, std::size_t N>
+    constexpr auto operator<=> (const array<T,N>& x, const array<T,N>& y)
+        -> decltype( x.elems[ 0 ] <=> y.elems[ 0 ] )
+    {
+        for( std::size_t i = 0; i < N; ++i )
+        {
+            auto r = x.elems[ i ] <=> y.elems[ i ];
+            if( r != 0 ) return r;
+        }
+
+        return std::strong_ordering::equal;
+    }
+
+    template<class T>
+    constexpr auto operator<=> (const array<T,0>& /*x*/, const array<T,0>& /*y*/)
+        -> std::strong_ordering
+    {
+        return std::strong_ordering::equal;
+    }
+
+# endif
+#endif
+
     // undocumented and obsolete
     template <typename T, std::size_t N>
     BOOST_DEPRECATED( "please use `elems` instead" )
@@ -404,25 +430,62 @@ namespace boost {
         return arg.elems;
     }
 
-    template <class It> std::size_t hash_range(It, It);
-
-    template<class T, std::size_t N>
-    std::size_t hash_value(const array<T,N>& arr)
+    template <size_t Idx, typename T, size_t N>
+    BOOST_CXX14_CONSTEXPR T &get(boost::array<T,N> &arr) BOOST_NOEXCEPT
     {
-        return boost::hash_range(arr.begin(), arr.end());
+        BOOST_STATIC_ASSERT_MSG ( Idx < N, "boost::get<>(boost::array &) index out of range" );
+        return arr[Idx];
     }
 
-   template <size_t Idx, typename T, size_t N>
-   BOOST_CXX14_CONSTEXPR T &get(boost::array<T,N> &arr) BOOST_NOEXCEPT {
-       BOOST_STATIC_ASSERT_MSG ( Idx < N, "boost::get<>(boost::array &) index out of range" );
-       return arr[Idx];
-       }
+    template <size_t Idx, typename T, size_t N>
+    BOOST_CONSTEXPR const T &get(const boost::array<T,N> &arr) BOOST_NOEXCEPT
+    {
+        BOOST_STATIC_ASSERT_MSG ( Idx < N, "boost::get<>(const boost::array &) index out of range" );
+        return arr[Idx];
+    }
 
-   template <size_t Idx, typename T, size_t N>
-   BOOST_CONSTEXPR const T &get(const boost::array<T,N> &arr) BOOST_NOEXCEPT {
-       BOOST_STATIC_ASSERT_MSG ( Idx < N, "boost::get<>(const boost::array &) index out of range" );
-       return arr[Idx];
-       }
+    template<class T, std::size_t N>
+    BOOST_CXX14_CONSTEXPR array<T, N> to_array( T const (&a)[ N ] )
+    {
+        array<T, N> r = {};
+
+        for( std::size_t i = 0; i < N; ++i )
+        {
+            r[ i ] = a[ i ];
+        }
+
+        return r;
+    }
+
+#if !defined(BOOST_NO_CXX11_RVALUE_REFERENCES)
+
+    template<class T, std::size_t N>
+    BOOST_CXX14_CONSTEXPR array<T, N> to_array( T (&&a)[ N ] )
+    {
+        array<T, N> r = {};
+
+        for( std::size_t i = 0; i < N; ++i )
+        {
+            r[ i ] = std::move( a[ i ] );
+        }
+
+        return r;
+    }
+
+    template<class T, std::size_t N>
+    BOOST_CXX14_CONSTEXPR array<T, N> to_array( T const (&&a)[ N ] )
+    {
+        array<T, N> r = {};
+
+        for( std::size_t i = 0; i < N; ++i )
+        {
+            r[ i ] = a[ i ];
+        }
+
+        return r;
+    }
+
+#endif
 
 } /* namespace boost */
 

test/Jamfile.v2

@@ -7,6 +7,41 @@ import testing ;
 import-search /boost/config/checks ;
 import config : requires ;
 
+project
+    : requirements
+
+        <library>/boost/array//boost_array
+        <library>/boost/core//boost_core
+
+        <warnings>extra
+
+        <toolset>msvc:<warnings-as-errors>on
+        <toolset>clang:<warnings-as-errors>on
+        <toolset>gcc:<warnings-as-errors>on
+
+        <toolset>gcc-4.6:<cxxflags>-Wno-missing-braces
+        <toolset>gcc-4.7:<cxxflags>-Wno-missing-braces
+
+        <toolset>gcc-4.6:<cxxflags>-Wno-missing-field-initializers
+        <toolset>gcc-4.7:<cxxflags>-Wno-missing-field-initializers
+        <toolset>gcc-4.8:<cxxflags>-Wno-missing-field-initializers
+        <toolset>gcc-4.9:<cxxflags>-Wno-missing-field-initializers
+
+        <toolset>gcc-4.6:<cxxflags>-Wno-type-limits
+        <toolset>gcc-4.7:<cxxflags>-Wno-type-limits
+        <toolset>gcc-10:<cxxflags>-Wno-type-limits
+
+        <toolset>clang:<cxxflags>-Wno-unnamed-type-template-args
+
+        <toolset>clang-3.5:<cxxflags>-Wno-missing-braces
+        <toolset>clang-3.6:<cxxflags>-Wno-missing-braces
+        <toolset>clang-3.7:<cxxflags>-Wno-missing-braces
+        <toolset>clang-3.8:<cxxflags>-Wno-missing-braces
+        <toolset>clang-3.9:<cxxflags>-Wno-missing-braces
+        <toolset>clang-4:<cxxflags>-Wno-missing-braces
+        <toolset>clang-5:<cxxflags>-Wno-missing-braces
+    ;
+
 #
 
 run array0.cpp ;
@@ -20,11 +55,13 @@ run array7.cpp ;
 
 compile array_constexpr.cpp ;
 
-compile-fail array_getfail1.cpp ;
-compile-fail array_getfail2.cpp ;
+compile-fail array_getfail1.cpp
+  : <warnings>off ;
+compile-fail array_getfail2.cpp
+  : <warnings>off ;
 
 run array_hash.cpp
-  : : : [ requires cxx11_noexcept ] ;
+  : : : <library>/boost/container_hash//boost_container_hash [ requires cxx11_noexcept ] ;
 
 #
 
@@ -45,7 +82,9 @@ run array_swap_test.cpp ;
 run array_swap_test2.cpp ;
 run array_eq_test.cpp ;
 run array_lt_test.cpp ;
+run array_thw_test.cpp ;
 run array_get_test.cpp ;
+run to_array_test.cpp ;
 
 # C++11 constexpr
 
@@ -59,8 +98,13 @@ compile array_get_test_cx.cpp ;
 
 # C++14 constexpr
 
+compile array_assign_test_cx.cpp ;
+compile array_access_test_cx2.cpp ;
+compile array_fill_test_cx.cpp ;
 compile array_eq_test_cx.cpp ;
 compile array_lt_test_cx.cpp ;
+compile array_thw_test_cx.cpp ;
+compile to_array_test_cx.cpp ;
 
 #
 

test/array0.cpp

@@ -44,7 +44,12 @@ void    RunTests()
     BOOST_TEST ( const_test_case.begin() == const_test_case.end());
     BOOST_TEST ( const_test_case.cbegin() == const_test_case.cend());
 
-    BOOST_TEST ( test_case.begin() != const_test_case.begin() );
+    // BOOST_TEST ( test_case.begin() != const_test_case.begin() );
+    //
+    // TR1 specified that begin() must return a unique value for zero-sized
+    // arrays. However, this makes constexpr unimplementable, and all standard
+    // libraries have converged on using nullptr instead (see LWG issue 2157.)
+
     if( test_case.data() == const_test_case.data() ) {
     //  Value of data is unspecified in TR1, so no requirement this test pass or fail
     //  However, it must compile!

test/array5.cpp

@@ -5,6 +5,8 @@
  * http://www.boost.org/LICENSE_1_0.txt)
  */
 
+#define BOOST_ALLOW_DEPRECATED_SYMBOLS // assign
+
 #include <iostream>
 #include <boost/array.hpp>
 

test/array6.cpp

@@ -5,12 +5,20 @@
  * http://www.boost.org/LICENSE_1_0.txt)
  */
 
+#define BOOST_ALLOW_DEPRECATED_SYMBOLS // get_c_array
+
+#include <boost/array.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
 #include <string>
 #include <iostream>
-#include <boost/array.hpp>
 #include <algorithm>
 
-#include <boost/core/lightweight_test_trait.hpp>
+#if defined(BOOST_GCC) && BOOST_GCC / 10000 == 13
+// false -Warray-bounds positive when using -fsanitize=undefined
+// restricted to GCC 13 because that's what is tested on Drone
+# pragma GCC diagnostic ignored "-Warray-bounds"
+#endif
 
 namespace {
     template< class T >

test/array7.cpp

@@ -5,6 +5,8 @@
  * http://www.boost.org/LICENSE_1_0.txt)
  */
 
+#define BOOST_ALLOW_DEPRECATED_SYMBOLS // std::get
+
 #include <string>
 #include <iostream>
 #include <boost/array.hpp>

test/array_access_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #define BOOST_ENABLE_ASSERT_HANDLER
 

test/array_access_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_access_test_cx2.cpp

@@ -0,0 +1,45 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config/workaround.hpp>
+#include <cstddef>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined")
+
+#else
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, std::size_t N> constexpr boost::array<T, N> modified( boost::array<T, N> a1 )
+{
+    a1.front() = 1;
+    a1[ 1 ] = 2;
+    a1.at( 2 ) = 3;
+    a1.back() = 4;
+
+    return a1;
+}
+
+template<class T> void test1()
+{
+    constexpr boost::array<T, 4> a1 = {};
+    constexpr boost::array<T, 4> a2 = modified( a1 );
+
+    STATIC_ASSERT( a2[0] == 1 );
+    STATIC_ASSERT( a2[1] == 2 );
+    STATIC_ASSERT( a2[2] == 3 );
+    STATIC_ASSERT( a2[3] == 4 );
+}
+
+int main()
+{
+    test1<int>();
+}
+
+#endif

test/array_assign_test.cpp

@@ -1,13 +1,18 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
+
+#define BOOST_ALLOW_DEPRECATED_SYMBOLS
+
+// assign is a deprecated nonstandard equivalent of fill
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
-// assign is a nonstandard equivalent of fill
-// it probably needs to be deprecated and removed
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
 
 template<class T, std::size_t N> void test()
 {

test/array_assign_test_cx.cpp

@@ -0,0 +1,54 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config/workaround.hpp>
+#include <cstddef>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined")
+
+#else
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, std::size_t N> constexpr boost::array<T, N> assigned( boost::array<T, N> const& a1 )
+{
+    boost::array<T, N> a2 = {};
+
+    a2 = a1;
+
+    return a2;
+}
+
+template<class T> void test1()
+{
+    constexpr boost::array<T, 4> a1 = {{ 1, 2, 3, 4 }};
+    constexpr boost::array<T, 4> a2 = assigned( a1 );
+
+    STATIC_ASSERT( a1[0] == a2[0] );
+    STATIC_ASSERT( a1[1] == a2[1] );
+    STATIC_ASSERT( a1[2] == a2[2] );
+    STATIC_ASSERT( a1[3] == a2[3] );
+}
+
+template<class T> void test2()
+{
+    constexpr boost::array<T, 0> a1 = {};
+    constexpr boost::array<T, 0> a2 = assigned( a1 );
+
+    (void)a1;
+    (void)a2;
+}
+
+int main()
+{
+    test1<int>();
+    test2<int>();
+}
+
+#endif

test/array_c_array_test.cpp

@@ -1,6 +1,8 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
+
+#define BOOST_ALLOW_DEPRECATED_SYMBOLS
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -8,8 +10,7 @@
 #include <boost/config/workaround.hpp>
 #include <cstddef>
 
-// c_array and get_c_array are nonstandard extensions
-// probably need to be deprecated and removed
+// c_array and get_c_array are deprecated nonstandard extensions
 
 template<class T, std::size_t N> void test()
 {

test/array_convert_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>

test/array_copy_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -44,11 +44,11 @@ template<class T> void test4()
 
 int main()
 {
-    // test1<int, 0>();
+    test1<int, 0>();
     test1<int, 1>();
     test1<int, 7>();
 
-    // test1<int const, 0>();
+    test1<int const, 0>();
     test1<int const, 1>();
     test1<int const, 7>();
 

test/array_copy_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_data_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>

test/array_data_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_elems_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>

test/array_eq_test.cpp

@@ -1,11 +1,15 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test()
 {
     {

test/array_eq_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_fill_test.cpp

@@ -1,11 +1,15 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test()
 {
     boost::array<T, N> a = {};

test/array_fill_test_cx.cpp

@@ -0,0 +1,51 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config/workaround.hpp>
+#include <cstddef>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined")
+
+#else
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, std::size_t N> constexpr boost::array<T, N> filled( T const& v )
+{
+    boost::array<T, N> r = {};
+
+    r.fill( v );
+
+    return r;
+}
+
+template<class T> void test1()
+{
+    constexpr boost::array<T, 4> a1 = filled<T, 4>( 7 );
+
+    STATIC_ASSERT( a1[0] == 7 );
+    STATIC_ASSERT( a1[1] == 7 );
+    STATIC_ASSERT( a1[2] == 7 );
+    STATIC_ASSERT( a1[3] == 7 );
+}
+
+template<class T> void test2()
+{
+    constexpr boost::array<T, 0> a1 = filled<T, 0>( 7 );
+
+    (void)a1;
+}
+
+int main()
+{
+    test1<int>();
+    test2<int>();
+}
+
+#endif

test/array_get_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>

test/array_get_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_init_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -8,6 +8,10 @@
 #include <boost/config/workaround.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test1()
 {
     boost::array<T, N> a = {{}};
@@ -46,11 +50,11 @@ template<class T> void test4()
 
 int main()
 {
-    // test1<int, 0>();
+    test1<int, 0>();
     test1<int, 1>();
     test1<int, 7>();
 
-    // test1<int const, 0>();
+    test1<int const, 0>();
     test1<int const, 1>();
     test1<int const, 7>();
 
@@ -58,7 +62,7 @@ int main()
     test2<int, 1>();
     test2<int, 7>();
 
-    // test2<int const, 0>();
+    test2<int const, 0>();
 
 #if BOOST_WORKAROUND(BOOST_MSVC, < 1910) || BOOST_WORKAROUND(BOOST_GCC, < 50000)
 

test/array_init_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>
@@ -56,7 +56,8 @@ template<class T> void test4()
 
 template<class T> void test5()
 {
-    // constexpr boost::array<T, 0> a = {{}};
+    constexpr boost::array<T, 0> a = {{}};
+    (void)a;
 }
 
 template<class T> void test6()

test/array_iterator_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -94,11 +94,11 @@ template<class T> void test2()
 
 int main()
 {
-    // test<int, 0>();
+    test<int, 0>();
     test<int, 1>();
     test<int, 7>();
 
-    // test<int const, 0>();
+    test<int const, 0>();
     test<int const, 1>();
     test<int const, 7>();
 

test/array_iterator_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>
@@ -39,20 +39,17 @@ template<class T> void test2()
 {
     constexpr boost::array<T, 0> a = {};
 
-    // iterator access is not constexpr for boost::array<T, 0>
-    // it is for std::array<T, 0>, though, so we should change it
-
     STATIC_ASSERT( a.begin() == a.end() );
     STATIC_ASSERT( a.cbegin() == a.cend() );
 }
 
 int main()
 {
-    // test1<int, 0>();
+    test1<int, 0>();
     test1<int, 1>();
     test1<int, 7>();
 
-    // test2<int>();
+    test2<int>();
 }
 
 #endif

test/array_lt_test.cpp

@@ -1,11 +1,15 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test()
 {
     {

test/array_lt_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_reverse_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -76,11 +76,11 @@ template<class T, std::size_t N> void test()
 
 int main()
 {
-    // test<int, 0>();
+    test<int, 0>();
     test<int, 1>();
     test<int, 7>();
 
-    // test<int const, 0>();
+    test<int const, 0>();
     test<int const, 1>();
     test<int const, 7>();
 

test/array_size_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
@@ -15,6 +15,8 @@ template<class T, std::size_t N> void test1()
         BOOST_TEST_EQ( a.size(), N );
         BOOST_TEST_EQ( a.empty(), N == 0 );
         BOOST_TEST_EQ( a.max_size(), N );
+
+        (void)a; // msvc-12.0
     }
 
     {
@@ -23,6 +25,8 @@ template<class T, std::size_t N> void test1()
         BOOST_TEST_EQ( a.size(), N );
         BOOST_TEST_EQ( a.empty(), N == 0 );
         BOOST_TEST_EQ( a.max_size(), N );
+
+        (void)a; // msvc-12.0
     }
 }
 
@@ -49,11 +53,11 @@ template<class T, std::size_t N> void test3()
 
 int main()
 {
-    // test1<int, 0>();
+    test1<int, 0>();
     test1<int, 1>();
     test1<int, 7>();
 
-    // test1<int const, 0>();
+    test1<int const, 0>();
     test1<int const, 1>();
     test1<int const, 7>();
 

test/array_size_test_cx.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/config.hpp>

test/array_swap_test.cpp

@@ -1,11 +1,15 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test()
 {
     boost::array<T, N> a1 = {};

test/array_swap_test2.cpp

@@ -1,11 +1,15 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test.hpp>
 #include <cstddef>
 
+#if defined(_MSC_VER)
+# pragma warning(disable: 4702) // unreachable code
+#endif
+
 template<class T, std::size_t N> void test()
 {
     boost::array<T, N> a1 = {};

test/array_thw_test.cpp

@@ -0,0 +1,102 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <cstddef>
+
+#if defined(__has_include)
+# if __has_include(<compare>)
+#  define HAS_COMPARE
+# endif
+#endif
+
+#if !defined(__cpp_impl_three_way_comparison)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because __cpp_impl_three_way_comparison is not defined" )
+int main() {}
+
+#elif !( __cpp_impl_three_way_comparison >= 201907L )
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because __cpp_impl_three_way_comparison is defined to " BOOST_STRINGIZE(__cpp_impl_three_way_comparison) )
+int main() {}
+
+#elif !defined(HAS_COMPARE)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because <compare> is not available" )
+int main() {}
+
+#else
+
+template<class T, std::size_t N> void test()
+{
+    constexpr auto eq = 0 <=> 0;
+    constexpr auto lt = 0 <=> 1;
+    constexpr auto gt = 1 <=> 0;
+
+    {
+        boost::array<T, N> const a1 = {};
+        boost::array<T, N> const a2 = {};
+
+        BOOST_TEST( ( a1 <=> a2 ) == eq );
+    }
+
+    {
+        boost::array<T, N> a1;
+        boost::array<T, N> a2;
+
+        a1.fill( 1 );
+        a2.fill( 1 );
+
+        BOOST_TEST( ( a1 <=> a2 ) == eq );
+    }
+
+    for( std::size_t i = 0; i < N; ++i )
+    {
+        boost::array<T, N> a1;
+        boost::array<T, N> a2;
+
+        a1.fill( 1 );
+        a2.fill( 1 );
+
+        a1[ i ] = 0;
+
+        BOOST_TEST( ( a1 <=> a2 ) == lt );
+
+        {
+            boost::array<T, N> const a3 = a1;
+            boost::array<T, N> const a4 = a2;
+
+            BOOST_TEST( ( a3 <=> a4 ) == lt );
+        }
+
+        a1[ i ] = 2;
+
+        BOOST_TEST( ( a1 <=> a2 ) == gt );
+
+        {
+            boost::array<T, N> const a3 = a1;
+            boost::array<T, N> const a4 = a2;
+
+            BOOST_TEST( ( a3 <=> a4 ) == gt );
+        }
+    }
+}
+
+int main()
+{
+    test<int, 0>();
+    test<int, 1>();
+    test<int, 7>();
+
+    test<float, 0>();
+    test<float, 1>();
+    test<float, 7>();
+
+    return boost::report_errors();
+}
+
+#endif

test/array_thw_test_cx.cpp

@@ -0,0 +1,81 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config/workaround.hpp>
+#include <cstddef>
+
+#if defined(__has_include)
+# if __has_include(<compare>)
+#  define HAS_COMPARE
+# endif
+#endif
+
+#if !defined(__cpp_impl_three_way_comparison)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because __cpp_impl_three_way_comparison is not defined" )
+int main() {}
+
+#elif !( __cpp_impl_three_way_comparison >= 201907L )
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because __cpp_impl_three_way_comparison is defined to " BOOST_STRINGIZE(__cpp_impl_three_way_comparison) )
+int main() {}
+
+#elif !defined(HAS_COMPARE)
+
+BOOST_PRAGMA_MESSAGE( "Test skipped because <compare> is not available" )
+int main() {}
+
+#else
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+template<class T, std::size_t N> void test1()
+{
+    constexpr auto eq = 0 <=> 0;
+
+    constexpr boost::array<T, N> a1 = {};
+    constexpr boost::array<T, N> a2 = {};
+
+    STATIC_ASSERT( ( a1 <=> a2 ) == eq );
+}
+
+template<class T> void test2()
+{
+    constexpr auto eq = 0 <=> 0;
+    constexpr auto lt = 0 <=> 1;
+    constexpr auto gt = 1 <=> 0;
+
+    {
+        constexpr boost::array<T, 4> a1 = {{ 1, 2, 3, 4 }};
+        constexpr boost::array<T, 4> a2 = {{ 1, 2, 3, 4 }};
+
+        STATIC_ASSERT( ( a1 <=> a2 ) == eq );
+    }
+    {
+        constexpr boost::array<T, 4> a1 = {{ 1, 2, 3, 4 }};
+        constexpr boost::array<T, 4> a2 = {{ 1, 2, 3, 5 }};
+
+        STATIC_ASSERT( ( a1 <=> a2 ) == lt );
+    }
+    {
+        constexpr boost::array<T, 4> a1 = {{ 1, 2, 3, 4 }};
+        constexpr boost::array<T, 4> a2 = {{ 1, 2, 3, 2 }};
+
+        STATIC_ASSERT( ( a1 <=> a2 ) == gt );
+    }
+}
+
+int main()
+{
+    test1<int, 0>();
+    test1<int, 1>();
+    test1<int, 7>();
+
+    test2<int>();
+}
+
+#endif

test/array_typedef_test.cpp

@@ -1,6 +1,6 @@
 // Copyright 2025 Peter Dimov
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 #include <boost/core/lightweight_test_trait.hpp>

test/quick.cpp

@@ -1,6 +1,6 @@
 // Copyright 2023 Peter Dimov.
 // Distributed under the Boost Software License, Version 1.0.
-// https://www.boost.org/LICENSE_1_0.txt)
+// https://www.boost.org/LICENSE_1_0.txt
 
 #include <boost/array.hpp>
 

test/to_array_test.cpp

@@ -0,0 +1,109 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/core/lightweight_test.hpp>
+#include <boost/config.hpp>
+#include <boost/config/workaround.hpp>
+#include <memory>
+#include <utility>
+
+boost::array<int, 3> f1()
+{
+    boost::array<int, 3> r = {{ 1, 2, 3 }};
+    return r;
+}
+
+boost::array<int, 3> const f2()
+{
+    boost::array<int, 3> r = {{ 1, 2, 3 }};
+    return r;
+}
+
+int main()
+{
+    {
+        int a[] = { 1, 2, 3 };
+
+        boost::array<int, 3> b = boost::to_array( a );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+
+    {
+        int const a[] = { 1, 2, 3 };
+
+        boost::array<int, 3> b = boost::to_array( a );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+
+    {
+        boost::array<int, 3> b = boost::to_array( f1().elems );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+
+    {
+        boost::array<int, 3> b = boost::to_array( f2().elems );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+
+#if BOOST_CXX_VERSION >= 201103L
+
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1910)
+    {
+        int a[] = { 1, 2, 3 };
+
+        boost::array<int, 3> b = boost::to_array( std::move( a ) );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+
+    {
+        int const a[] = { 1, 2, 3 };
+
+        boost::array<int, 3> b = boost::to_array( std::move( a ) );
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+#endif
+
+#if !BOOST_WORKAROUND(BOOST_GCC, < 40900) && !BOOST_WORKAROUND(BOOST_CLANG_VERSION, < 30800)
+    {
+        boost::array<int, 3> b = boost::to_array({ 1, 2, 3 });
+
+        BOOST_TEST_EQ( b[0], 1 );
+        BOOST_TEST_EQ( b[1], 2 );
+        BOOST_TEST_EQ( b[2], 3 );
+    }
+#endif
+
+#if !BOOST_WORKAROUND(BOOST_MSVC, < 1920)
+    {
+        std::unique_ptr<int> a[] = { {}, {}, {} };
+
+        boost::array<std::unique_ptr<int>, 3> b = boost::to_array( std::move( a ) );
+
+        (void)b;
+    }
+#endif
+
+#endif
+
+    return boost::report_errors();
+}

test/to_array_test_cx.cpp

@@ -0,0 +1,32 @@
+// Copyright 2025 Peter Dimov
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+
+#include <boost/array.hpp>
+#include <boost/config.hpp>
+#include <boost/config/pragma_message.hpp>
+#include <boost/config/workaround.hpp>
+#include <cstddef>
+
+#if defined(BOOST_NO_CXX14_CONSTEXPR)
+
+BOOST_PRAGMA_MESSAGE("Test skipped because BOOST_NO_CXX14_CONSTEXPR is defined")
+
+#else
+
+#define STATIC_ASSERT(...) static_assert(__VA_ARGS__, #__VA_ARGS__)
+
+int main()
+{
+    {
+        constexpr int a[] = { 1, 2, 3, 4 };
+        constexpr boost::array<int, 4> b = boost::to_array( a );
+
+        STATIC_ASSERT( b[0] == 1 );
+        STATIC_ASSERT( b[1] == 2 );
+        STATIC_ASSERT( b[2] == 3 );
+        STATIC_ASSERT( b[3] == 4 );
+    }
+}
+
+#endif