[libcxx-commits] [libcxx] [libc++] Implement P0429R9 `std::flat_map` (PR #98643)

[Louis Dionne via libcxx-commits]

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@@ -0,0 +1,104 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// UNSUPPORTED: c++03, c++11, c++14, c++17, c++20
+
+// <flat_map>
+
+// flat_map& operator=(flat_map&&);
+// Preserves the class invariant for the moved-from flat_map.
+
+#include <algorithm>
+#include <cassert>
+#include <compare>
+#include <flat_map>
+#include <functional>
+#include <utility>
+#include <vector>
+
+#include "../helpers.h"
+#include "test_macros.h"
+
+struct MoveNegates {
+  int value_    = 0;
+  MoveNegates() = default;
+  MoveNegates(int v) : value_(v) {}
+  MoveNegates(MoveNegates&& rhs) : value_(rhs.value_) { rhs.value_ = -rhs.value_; }
+  MoveNegates& operator=(MoveNegates&& rhs) {
+    value_     = rhs.value_;
+    rhs.value_ = -rhs.value_;
+    return *this;
+  }
+  ~MoveNegates()                             = default;
+  auto operator<=>(const MoveNegates&) const = default;
+};
+
+struct MoveClears {
+  int value_   = 0;
+  MoveClears() = default;
+  MoveClears(int v) : value_(v) {}
+  MoveClears(MoveClears&& rhs) : value_(rhs.value_) { rhs.value_ = 0; }
+  MoveClears& operator=(MoveClears&& rhs) {
+    value_     = rhs.value_;
+    rhs.value_ = 0;
+    return *this;
+  }
+  ~MoveClears()                             = default;
+  auto operator<=>(const MoveClears&) const = default;
+};
+
+int main(int, char**) {
+  auto value_eq = [](auto&& p, auto&& q) { return p.first == q.first; };
+  {
+    const std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {6, 6}, {7, 7}, {8, 8}};
+    using M = std::flat_map<MoveNegates, int, std::less<MoveNegates>, std::vector<MoveNegates>>;
+    M m     = M(expected, expected + 8);
+    M m2    = M(expected, expected + 3);
+
+    m2 = std::move(m);
+
+    assert(std::equal(m2.begin(), m2.end(), expected, expected + 8));
+    LIBCPP_ASSERT(m.empty());
+    assert(std::is_sorted(m.begin(), m.end(), m.value_comp()));          // still sorted
+    assert(std::adjacent_find(m.begin(), m.end(), value_eq) == m.end()); // still contains no duplicates
+    m.insert({1, 1});
+    m.insert({2, 2});
+    assert(m.contains(1));
+    assert(m.find(2) != m.end());
+  }
+  {
+    const std::pair<int, int> expected[] = {{1, 1}, {2, 2}, {3, 3}, {4, 4}, {5, 5}, {6, 6}, {7, 7}, {8, 8}};
+    using M = std::flat_map<MoveClears, int, std::less<MoveClears>, std::vector<MoveClears>>;
+    M m     = M(expected, expected + 8);
+    M m2    = M(expected, expected + 3);
+
+    m2 = std::move(m);
+
+    assert(std::equal(m2.begin(), m2.end(), expected, expected + 8));
+    LIBCPP_ASSERT(m.empty());
+    assert(std::is_sorted(m.begin(), m.end(), m.value_comp()));          // still sorted
+    assert(std::adjacent_find(m.begin(), m.end(), value_eq) == m.end()); // still contains no duplicates
+    m.insert({1, 1});
+    m.insert({2, 2});
+    assert(m.contains(1));
+    assert(m.find(2) != m.end());
+  }
+  {
+    // moved-from object maintains invariant if one of underlying container does not clear after move
+    using M = std::flat_map<int, int, std::less<>, std::vector<int>, CopyOnlyVector<int>>;
+    M m1    = M({1, 2, 3}, {1, 2, 3});
+    M m2    = M({1, 2}, {1, 2});
+    m2      = std::move(m1);
+    assert(m2.size() == 3);
+    assert(m1.keys().size() == m1.values().size());
----------------
ldionne wrote:

Would it be worth extracting this into a function like `check_invariants` that would check
1. `keys.size() == values.size()`
2. sorted
3. uniqued

You probably have similar tests in a bunch of places, and could use that function instead. To help find these occurrences, you could grep for `adjacent_find` and `is_sorted`, and maybe e.g. `invariant` or something like that.

https://github.com/llvm/llvm-project/pull/98643