[libc++] Implement P2447 "std::span convertible from std::initializer…

…_list".
Quuxplusone · Oct 3, 2021 · 59493f0 · 59493f0
1 parent e462ff5
commit 59493f0
Show file tree

Hide file tree

Showing 4 changed files with 13 additions and 5 deletions.
diff --git a/libcxx/include/module.modulemap b/libcxx/include/module.modulemap
@@ -735,6 +735,7 @@ module std [system] {
   }
   module span {
     header "span"
+    export initializer_list
     export ranges.__ranges.enable_borrowed_range
     export version
   }

diff --git a/libcxx/include/span b/libcxx/include/span
@@ -68,6 +68,7 @@ public:
         constexpr span(const array<value_type, N>& arr) noexcept;
     template<class R>
       constexpr explicit(extent != dynamic_extent) span(R&& r);
+    constexpr explicit(extent != dynamic_extent) span(initializer_list<value_type> il) noexcept;
     constexpr span(const span& other) noexcept = default;
     template <class OtherElementType, size_t OtherExtent>
         constexpr explicit(Extent != dynamic_extent) span(const span<OtherElementType, OtherExtent>& s) noexcept;
@@ -138,6 +139,7 @@ template<class R>
 #include <__ranges/size.h>
 #include <array>        // for array
 #include <cstddef>      // for byte
+#include <initializer_list>
 #include <iterator>     // for iterators
 #include <limits>
 #include <type_traits>  // for remove_cv, etc
@@ -256,6 +258,10 @@ public:
     }
 #endif
 
+    constexpr explicit span(initializer_list<value_type> __il) requires is_const_v<element_type> : __data(__il.begin()) {
+      _LIBCPP_ASSERT(__il.size() == _Extent, "size mismatch in span's constructor (initializer list)");
+    }
+
     template <class _OtherElementType>
     _LIBCPP_INLINE_VISIBILITY
         constexpr span(const span<_OtherElementType, _Extent>& __other,
@@ -440,6 +446,9 @@ public:
     constexpr span(_Range&& __r) : __data{ranges::data(__r)}, __size{ranges::size(__r)} {}
 #  endif
 
+    constexpr span(initializer_list<value_type> __il) requires is_const_v<element_type>
+        : __data(__il.begin()), __size(__il.size()) {}
+
     template <class _OtherElementType, size_t _OtherExtent>
     _LIBCPP_INLINE_VISIBILITY
         constexpr span(const span<_OtherElementType, _OtherExtent>& __other,

diff --git a/libcxx/test/std/containers/views/span.cons/array.pass.cpp b/libcxx/test/std/containers/views/span.cons/array.pass.cpp
@@ -94,9 +94,7 @@ constexpr bool testSpan()
     assert(s4.data() == val && s4.size() == 2);
 
     std::span<const int> s5 = {{1,2}};
-    std::span<const int, 2> s6 = {{1,2}};
     assert(s5.size() == 2);  // and it dangles
-    assert(s6.size() == 2);  // and it dangles
 
     return true;
 }

diff --git a/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp b/libcxx/test/std/containers/views/span.cons/initializer_list.pass.cpp
@@ -28,9 +28,9 @@ constexpr int countn(std::span<const Sink, N> sp) {
 
 constexpr bool test() {
     Sink a[10];
-    assert(count({a}) == 10);
-    assert(count({a, a+10}) == 10);
-    assert(countn<10>({a}) == 10);
+    assert(count({a}) == 1);
+    assert(count({a, a+10}) == 2);
+    assert(count({a, a+1, a+2}) == 3);
     return true;
 }