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ARROW-11998: [C++] Make it easier to create vectors of move-only data types for tests #9734

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ARROW-11998: [C++] Make it easier to create vectors of move-only data types for tests #9734

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6cf630e
Provide easier way to emplace-map-construct vectors
pitrou Mar 16, 2021
14d57e0
Added back in test
westonpace Mar 17, 2021
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12 changes: 12 additions & 0 deletions cpp/src/arrow/util/functional.h
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Expand Up @@ -126,5 +126,17 @@ class FnOnce<R(A...)> {
std::unique_ptr<Impl> impl_;
};

/// A callable object that simply forwards to T's constructor.
///
/// This allows passing `Constructor<T>()` as a callable argument for applying
/// the T constructor without hand-writing a lambda.
template <typename T>
struct Constructor {
template <typename... Values>
T operator()(Values&&... values) {
return T(std::forward<Values>(values)...);
}
};

} // namespace internal
} // namespace arrow
20 changes: 20 additions & 0 deletions cpp/src/arrow/util/stl_util_test.cc
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Expand Up @@ -21,6 +21,9 @@
#include <gmock/gmock.h>
#include <gtest/gtest.h>

#include "arrow/result.h"
#include "arrow/testing/gtest_util.h"
#include "arrow/util/functional.h"
#include "arrow/util/sort.h"
#include "arrow/util/string.h"
#include "arrow/util/vector.h"
Expand Down Expand Up @@ -92,5 +95,22 @@ TEST(StlUtilTest, ArgSortPermute) {
ExpectSortPermutation({b, c, d, e, a, f}, {4, 0, 1, 2, 3, 5}, 2);
}

TEST(StlUtilTest, MapEmplaceBack) {
auto all_good = EmplacedMappedVector<Result<MoveOnlyDataType>>(
Constructor<MoveOnlyDataType>(), 1, 2, 3);

ASSERT_EQ(all_good[0].ValueUnsafe(), 1);
ASSERT_EQ(all_good[1].ValueUnsafe(), 2);
ASSERT_EQ(all_good[2].ValueUnsafe(), 3);
ASSERT_EQ(all_good.size(), 3);

auto some_bad = EmplacedVector<Result<MoveOnlyDataType>>(
MoveOnlyDataType(1), Status::Invalid("XYZ"), Status::IOError("XYZ"));

ASSERT_EQ(some_bad[0].ValueUnsafe(), 1);
ASSERT_TRUE(some_bad[1].status().IsInvalid());
ASSERT_TRUE(some_bad[2].status().IsIOError());
}

} // namespace internal
} // namespace arrow
38 changes: 38 additions & 0 deletions cpp/src/arrow/util/vector.h
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Expand Up @@ -81,5 +81,43 @@ std::vector<T> FilterVector(std::vector<T> values, Predicate&& predicate) {
return values;
}

template <typename T, typename Fn>
void MapEmplaceBack(std::vector<T>* out, Fn&& fn) {}

template <typename T, typename Fn, typename Head, typename... Values>
void MapEmplaceBack(std::vector<T>* out, Fn&& fn, Head&& value, Values&&... tail_values) {
out->emplace_back(fn(std::forward<Head>(value)));
MapEmplaceBack(out, std::forward<Fn>(fn), std::forward<Values>(tail_values)...);
}

template <typename T>
void EmplaceBack(std::vector<T>* out) {}

template <typename T, typename Head, typename... Values>
void EmplaceBack(std::vector<T>* out, Head&& value, Values&&... tail_values) {
out->emplace_back(std::forward<Head>(value));
EmplaceBack(out, std::forward<Values>(tail_values)...);
}

// Construct a vector by emplacing with each of the provided values.
// Note this is less flexible than manual calls to emplace_back(), since
// only 1-argument constructors can be invoked.
template <typename T, typename... Values>
std::vector<T> EmplacedVector(Values&&... values) {
std::vector<T> result;
result.reserve(sizeof...(values));
EmplaceBack(&result, std::forward<Values>(values)...);
return result;
}

// Like EmplacedVector, but emplace the result of calling `Fn` on the `values`.
template <typename T, typename Fn, typename... Values>
std::vector<T> EmplacedMappedVector(Fn&& fn, Values&&... values) {
std::vector<T> result;
result.reserve(sizeof...(values));
MapEmplaceBack(&result, std::forward<Fn>(fn), std::forward<Values>(values)...);
return result;
}

} // namespace internal
} // namespace arrow