taepper commented on code in PR #51328:
URL: https://github.com/apache/arrow/pull/51328#discussion_r4009369884
##########
cpp/src/arrow/util/cache_internal.h:
##########
@@ -167,42 +166,42 @@ struct ThreadUnsafeMemoizer {
};
template <template <typename...> class Cache, template <typename...> class
MemoizerType,
- typename Func, typename Key =
std::decay_t<call_traits::argument_type<0, Func>>,
- typename Value = std::decay_t<std::invoke_result_t<Func, const
Key&>>,
- typename Memoizer = MemoizerType<Key, Value, Cache<Key, Value>,
Func>,
- typename RetType = typename Memoizer::RetType>
-static std::function<RetType(const Key&)> Memoize(Func&& func, int32_t
cache_capacity) {
+ typename Key, typename Func>
+static auto Memoize(Func&& func, int32_t cache_capacity) {
+ using Value = std::decay_t<std::invoke_result_t<Func, const Key&>>;
+ using Memoizer = MemoizerType<Key, Value, Cache<Key, Value>, Func>;
+ using RetType = typename Memoizer::RetType;
+
// std::function<> requires copy constructibility
struct {
RetType operator()(const Key& key) const { return (*memoized_)(key); }
std::shared_ptr<Memoizer> memoized_;
} shared_memoized = {
std::make_shared<Memoizer>(std::forward<Func>(func), cache_capacity)};
- return shared_memoized;
+ return std::function<RetType(const Key&)>(std::move(shared_memoized));
Review Comment:
Maybe I am understanding the code wrong, but I thought the change is
equivalent.
The previous version had the function declaration:
`static std::function<RetType(const Key&)> Memoize(...)`
whereas now we have
`static auto Memoize(...)`
so all I did in the return statement was changing the _implicit_ conversion
to a `std::function` to an explicit one
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