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Posted to github@arrow.apache.org by GitBox <gi...@apache.org> on 2021/07/15 18:07:12 UTC

[GitHub] [arrow] lidavidm commented on a change in pull request #10726: ARROW-13347: [C++] Remove compile time parsing from EnumType

lidavidm commented on a change in pull request #10726:
URL: https://github.com/apache/arrow/pull/10726#discussion_r670696529



##########
File path: cpp/src/arrow/util/enum.h
##########
@@ -43,68 +42,51 @@ constexpr bool CaseInsensitiveEquals(util::string_view l, util::string_view r) {
   return l.size() == r.size() && CaseInsensitiveEquals(l.data(), r.data(), l.size());
 }
 
-constexpr const char* SkipWhitespace(const char* raw) {
-  return *raw == '\0' || !IsSpace(*raw) ? raw : SkipWhitespace(raw + 1);
-}
+}  // namespace internal
 
-constexpr const char* SkipNonWhitespace(const char* raw) {
-  return *raw == '\0' || IsSpace(*raw) ? raw : SkipNonWhitespace(raw + 1);
-}
+template <int N>
+struct EnumStrings {
+  template <int M>
+  static constexpr bool assert_count() {
+    static_assert(M == N, "Incorrect number of enum strings provided");
+    return false;
+  }
 
-constexpr size_t TokenSize(const char* token_start) {
-  return SkipNonWhitespace(token_start) - token_start;
-}
+  template <typename... Strs>
+  constexpr EnumStrings(const Strs&... strs)  // NOLINT runtime/explicit
+      : dummy_{assert_count<sizeof...(Strs)>()}, strings_{util::string_view(strs)...} {}
 
-constexpr size_t NextTokenStart(const char* raw, size_t token_start) {
-  return SkipWhitespace(SkipNonWhitespace(raw + token_start)) - raw;
-}
+  constexpr int GetIndex(util::string_view repr, int i = 0) const {
+    return i == N ? -1
+                  : internal::CaseInsensitiveEquals(strings_[i], repr)
+                        ? i
+                        : GetIndex(repr, i + 1);
+  }
 
-template <typename Raw, size_t... Offsets>
-struct EnumTypeImpl {
-  static constexpr int kSize = sizeof...(Offsets);
+  using value_type = util::string_view;
+  using const_iterator = const util::string_view*;
 
-  static constexpr util::string_view kValueStrs[sizeof...(Offsets)] = {
-      {Raw::kValues + Offsets, TokenSize(Raw::kValues + Offsets)}...};
+  constexpr int size() const { return N; }
+  constexpr const util::string_view* data() const { return strings_; }
+  constexpr const_iterator begin() const { return data(); }
+  constexpr const_iterator end() const { return begin() + size(); }
+  constexpr util::string_view operator[](int i) const { return strings_[i]; }
 
-  static constexpr int GetIndex(util::string_view repr, int i = 0) {
-    return i == kSize
-               ? -1
-               : CaseInsensitiveEquals(kValueStrs[i], repr) ? i : GetIndex(repr, i + 1);
-  }
+  bool dummy_;
+  util::string_view strings_[N];  // NOLINT modernize

Review comment:
       We can't use std::array since its methods aren't constexpr until C++17?




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