FTL: Tidy up API

Move array_traits.h to details, and rename enum_cast to its proposed
C++23 counterpart.

Bug: 185536303
Test: ftl_test
Change-Id: I432448d388d388491066ef37db05c5b9d67550bc

6 files changed, 34 insertions, 32 deletions

diff --git a/include/ftl/Flags.h b/include/ftl/Flags.h
index ae708313fd..932af2d9f9 100644
--- a/include/ftl/Flags.h
+++ b/include/ftl/Flags.h
@@ -209,12 +209,12 @@ namespace flag_operators {
 
 template <typename F, typename = std::enable_if_t<ftl::is_scoped_enum_v<F>>>
 inline Flags<F> operator~(F f) {
-    return static_cast<F>(~ftl::enum_cast(f));
+    return static_cast<F>(~ftl::to_underlying(f));
 }
 
 template <typename F, typename = std::enable_if_t<ftl::is_scoped_enum_v<F>>>
 Flags<F> operator|(F lhs, F rhs) {
-    return static_cast<F>(ftl::enum_cast(lhs) | ftl::enum_cast(rhs));
+    return static_cast<F>(ftl::to_underlying(lhs) | ftl::to_underlying(rhs));
 }
 
 } // namespace flag_operators
diff --git a/include/ftl/array_traits.h b/include/ftl/details/array_traits.h
index 1265fa15fe..16e63eca74 100644
--- a/include/ftl/array_traits.h
+++ b/include/ftl/details/array_traits.h
@@ -21,9 +21,9 @@
 #include <new>
 #include <type_traits>
 
-#define FTL_ARRAY_TRAIT(T, U) using U = typename ArrayTraits<T>::U
+#define FTL_ARRAY_TRAIT(T, U) using U = typename details::ArrayTraits<T>::U
 
-namespace android::ftl {
+namespace android::ftl::details {
 
 template <typename T>
 struct ArrayTraits {
@@ -132,4 +132,4 @@ struct ArrayComparators {
   }
 };
 
-}  // namespace android::ftl
+}  // namespace android::ftl::details
diff --git a/include/ftl/enum.h b/include/ftl/enum.h
index dfe3a0976b..5234c051b1 100644
--- a/include/ftl/enum.h
+++ b/include/ftl/enum.h
@@ -87,11 +87,13 @@ inline constexpr bool is_scoped_enum_v = is_scoped_enum<T>::value;
 
 // Shorthand for casting an enumerator to its integral value.
 //
+// TODO: Replace with std::to_underlying in C++23.
+//
 //   enum class E { A, B, C };
-//   static_assert(ftl::enum_cast(E::B) == 1);
+//   static_assert(ftl::to_underlying(E::B) == 1);
 //
 template <typename E>
-constexpr auto enum_cast(E v) {
+constexpr auto to_underlying(E v) {
   return static_cast<std::underlying_type_t<E>>(v);
 }
 
@@ -137,19 +139,19 @@ struct enum_end {
 
 template <typename E>
 struct enum_end<E, std::void_t<decltype(E::ftl_last)>> {
-  static constexpr E value = E{enum_cast(E::ftl_last) + 1};
+  static constexpr E value = E{to_underlying(E::ftl_last) + 1};
 };
 
 template <typename E>
 inline constexpr E enum_end_v = enum_end<E>::value;
 
 template <typename E>
-inline constexpr E enum_last_v = E{enum_cast(enum_end_v<E>) - 1};
+inline constexpr E enum_last_v = E{to_underlying(enum_end_v<E>) - 1};
 
 template <typename E>
 struct enum_size {
-  static constexpr auto kBegin = enum_cast(enum_begin_v<E>);
-  static constexpr auto kEnd = enum_cast(enum_end_v<E>);
+  static constexpr auto kBegin = to_underlying(enum_begin_v<E>);
+  static constexpr auto kEnd = to_underlying(enum_end_v<E>);
   static_assert(kBegin < kEnd, "Invalid range");
 
   static constexpr std::size_t value = kEnd - kBegin;
@@ -174,7 +176,7 @@ struct EnumRange;
 
 template <typename E, template <E> class F, typename T, T... Vs>
 struct EnumRange<E, F, std::integer_sequence<T, Vs...>> {
-  static constexpr auto kBegin = enum_cast(enum_begin_v<E>);
+  static constexpr auto kBegin = to_underlying(enum_begin_v<E>);
   static constexpr auto kSize = enum_size_v<E>;
 
   using R = decltype(F<E{}>::value);
@@ -194,7 +196,7 @@ struct FlagName {
   using E = decltype(I);
   using U = std::underlying_type_t<E>;
 
-  static constexpr E V{U{1} << enum_cast(I)};
+  static constexpr E V{U{1} << to_underlying(I)};
   static constexpr auto value = ftl_enum<E, V>();
 };
 
@@ -237,10 +239,10 @@ constexpr std::string_view enum_name() {
 //
 template <typename E>
 constexpr std::optional<std::string_view> enum_name(E v) {
-  const auto value = enum_cast(v);
+  const auto value = to_underlying(v);
 
-  constexpr auto kBegin = enum_cast(enum_begin_v<E>);
-  constexpr auto kLast = enum_cast(enum_last_v<E>);
+  constexpr auto kBegin = to_underlying(enum_begin_v<E>);
+  constexpr auto kLast = to_underlying(enum_last_v<E>);
   if (value < kBegin || value > kLast) return {};
 
   constexpr auto kRange = details::EnumRange<E, details::EnumName>{};
@@ -256,7 +258,7 @@ constexpr std::optional<std::string_view> enum_name(E v) {
 //
 template <typename E>
 constexpr std::optional<std::string_view> flag_name(E v) {
-  const auto value = enum_cast(v);
+  const auto value = to_underlying(v);
 
   // TODO: Replace with std::popcount and std::countr_zero in C++20.
   if (__builtin_popcountl(value) != 1) return {};
@@ -277,7 +279,7 @@ inline std::string enum_string(E v) {
   if (const auto name = enum_name(v)) {
     return std::string(*name);
   }
-  return to_string(enum_cast(v));
+  return to_string(to_underlying(v));
 }
 
 // Returns a stringified flag enumerator, or its integral value if not named.
@@ -293,7 +295,7 @@ inline std::string flag_string(E v) {
     return std::string(*name);
   }
   constexpr auto radix = sizeof(E) == 1 ? Radix::kBin : Radix::kHex;
-  return to_string(enum_cast(v), radix);
+  return to_string(to_underlying(v), radix);
 }
 
 }  // namespace android::ftl
diff --git a/include/ftl/small_vector.h b/include/ftl/small_vector.h
index 65a953670d..03587e35ac 100644
--- a/include/ftl/small_vector.h
+++ b/include/ftl/small_vector.h
@@ -16,7 +16,7 @@
 
 #pragma once
 
-#include <ftl/array_traits.h>
+#include <ftl/details/array_traits.h>
 #include <ftl/static_vector.h>
 
 #include <algorithm>
@@ -73,7 +73,7 @@ struct is_small_vector;
 //   assert(strings[2] == "???");
 //
 template <typename T, std::size_t N>
-class SmallVector final : ArrayTraits<T>, ArrayComparators<SmallVector> {
+class SmallVector final : details::ArrayTraits<T>, details::ArrayComparators<SmallVector> {
   using Static = StaticVector<T, N>;
   using Dynamic = SmallVector<T, 0>;
 
@@ -266,12 +266,12 @@ class SmallVector final : ArrayTraits<T>, ArrayComparators<SmallVector> {
 
 // Partial specialization without static storage.
 template <typename T>
-class SmallVector<T, 0> final : ArrayTraits<T>,
-                                ArrayIterators<SmallVector<T, 0>, T>,
+class SmallVector<T, 0> final : details::ArrayTraits<T>,
+                                details::ArrayIterators<SmallVector<T, 0>, T>,
                                 std::vector<T> {
-  using ArrayTraits<T>::construct_at;
+  using details::ArrayTraits<T>::construct_at;
 
-  using Iter = ArrayIterators<SmallVector, T>;
+  using Iter = details::ArrayIterators<SmallVector, T>;
   using Impl = std::vector<T>;
 
   friend Iter;
diff --git a/include/ftl/static_vector.h b/include/ftl/static_vector.h
index cd7b92a758..b7f8c29dec 100644
--- a/include/ftl/static_vector.h
+++ b/include/ftl/static_vector.h
@@ -16,7 +16,7 @@
 
 #pragma once
 
-#include <ftl/array_traits.h>
+#include <ftl/details/array_traits.h>
 #include <ftl/initializer_list.h>
 
 #include <algorithm>
@@ -73,14 +73,14 @@ constexpr struct IteratorRangeTag {
 //   assert(strings[2] == "???");
 //
 template <typename T, std::size_t N>
-class StaticVector final : ArrayTraits<T>,
-                           ArrayIterators<StaticVector<T, N>, T>,
-                           ArrayComparators<StaticVector> {
+class StaticVector final : details::ArrayTraits<T>,
+                           details::ArrayIterators<StaticVector<T, N>, T>,
+                           details::ArrayComparators<StaticVector> {
   static_assert(N > 0);
 
-  using ArrayTraits<T>::construct_at;
+  using details::ArrayTraits<T>::construct_at;
 
-  using Iter = ArrayIterators<StaticVector, T>;
+  using Iter = details::ArrayIterators<StaticVector, T>;
   friend Iter;
 
   // There is ambiguity when constructing from two iterator-like elements like pointers:
diff --git a/libs/ftl/enum_test.cpp b/libs/ftl/enum_test.cpp
index 1fd43abbc6..d8ce7a5e7b 100644
--- a/libs/ftl/enum_test.cpp
+++ b/libs/ftl/enum_test.cpp
@@ -72,7 +72,7 @@ enum class Planet : std::uint8_t {
   kNeptune
 };
 
-constexpr Planet kPluto{ftl::enum_cast(Planet::kNeptune) + 1};  // Honorable mention.
+constexpr Planet kPluto{ftl::to_underlying(Planet::kNeptune) + 1};  // Honorable mention.
 
 static_assert(ftl::enum_begin_v<Planet> == Planet::kMercury);
 static_assert(ftl::enum_last_v<Planet> == Planet::kNeptune);