bkietz commented on a change in pull request #10397:
URL: https://github.com/apache/arrow/pull/10397#discussion_r644278039
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File path: cpp/src/arrow/util/async_generator.h
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@@ -258,43 +258,27 @@ class MappingGenerator {
/// Note: Errors returned from the `map` function will be propagated
///
/// If the source generator is async-reentrant then this generator will be also
-template <typename T, typename V>
-AsyncGenerator<V> MakeMappedGenerator(AsyncGenerator<T> source_generator,
- std::function<Result<V>(const T&)> map) {
- std::function<Future<V>(const T&)> future_map = [map](const T& val) ->
Future<V> {
- return Future<V>::MakeFinished(map(val));
- };
- return MappingGenerator<T, V>(std::move(source_generator),
std::move(future_map));
-}
-template <typename T, typename V>
-AsyncGenerator<V> MakeMappedGenerator(AsyncGenerator<T> source_generator,
- std::function<V(const T&)> map) {
- std::function<Future<V>(const T&)> maybe_future_map = [map](const T& val) ->
Future<V> {
- return Future<V>::MakeFinished(map(val));
- };
- return MappingGenerator<T, V>(std::move(source_generator),
std::move(maybe_future_map));
-}
-template <typename T, typename V>
-AsyncGenerator<V> MakeMappedGenerator(AsyncGenerator<T> source_generator,
- std::function<Future<V>(const T&)> map) {
- return MappingGenerator<T, V>(std::move(source_generator), std::move(map));
-}
-
-template <typename V, typename T, typename MapFunc>
-AsyncGenerator<V> MakeMappedGenerator(AsyncGenerator<T> source_generator,
MapFunc map) {
+template <typename T, typename MapFn,
+ typename Mapped = detail::result_of_t<MapFn(const T&)>,
+ typename V = typename EnsureFuture<Mapped>::type::ValueType>
+AsyncGenerator<V> MakeMappedGenerator(AsyncGenerator<T> source_generator,
MapFn map) {
struct MapCallback {
- MapFunc map;
+ MapFn map_;
- Future<V> operator()(const T& val) { return EnsureFuture(map(val)); }
+ Future<V> operator()(const T& val) { return EnsureFuture(map_(val)); }
+
+ Future<V> EnsureFuture(V mapped) {
+ return Future<V>::MakeFinished(std::move(mapped));
+ }
- Future<V> EnsureFuture(Result<V> val) {
- return Future<V>::MakeFinished(std::move(val));
+ Future<V> EnsureFuture(Result<V> mapped) {
+ return Future<V>::MakeFinished(std::move(mapped));
}
- Future<V> EnsureFuture(V val) { return
Future<V>::MakeFinished(std::move(val)); }
- Future<V> EnsureFuture(Future<V> val) { return val; }
+
+ Future<V> EnsureFuture(Future<V> mapped) { return mapped; }
Review comment:
I'll extract a helper function
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