Merge pull request bemanproject#69 from steve-downey/hash

Implement std::hash for beman::optional

Author: steve-downey

include/beman/optional26/optional.hpp

@@ -1147,4 +1147,21 @@ class optional<T&> {
 
 } // namespace beman::optional26
 
+namespace std {
+template <typename T>
+    requires requires(T a) {
+        { std::hash<remove_const_t<T>>{}(a) } -> std::convertible_to<std::size_t>;
+    }
+struct hash<beman::optional26::optional<T>> {
+    static_assert(!is_reference_v<T>, "hash is not enabled for reference types");
+    size_t operator()(const beman::optional26::optional<T>& o) const
+        noexcept(noexcept(hash<remove_const_t<T>>{}(*o))) {
+        if (o) {
+            return std::hash<std::remove_const_t<T>>{}(*o);
+        } else {
+            return 0;
+        }
+    }
+};
+} // namespace std
 #endif // BEMAN_OPTIONAL26_OPTIONAL_HPP

src/beman/optional26/tests/optional.t.cpp

@@ -10,6 +10,7 @@
 #include <functional>
 #include <ranges>
 #include <tuple>
+#include <algorithm>
 
 #include <gtest/gtest.h>
 
@@ -596,7 +597,7 @@ TEST(OptionalTest, RangeTest) {
     }
 }
 
-TEST(ViewMaybeTest, Constructors) {
+TEST(OptionalTest, RangeConstructors) {
     std::ranges::single_view<std::optional<int>> s;
     std::ranges::single_view<std::optional<int>> s2{s};
     std::ranges::single_view<std::optional<int>> s3{std::optional<int>{}};
@@ -610,7 +611,7 @@ TEST(ViewMaybeTest, Constructors) {
     std::ignore = n3;
 }
 
-TEST(ViewMaybeTest, ConceptCheckRef) {
+TEST(OptionalTest, ConceptCheckRef) {
     static_assert(std::ranges::range<beman::optional26::optional<int&>>);
     static_assert(std::ranges::view<beman::optional26::optional<int&>>);
     static_assert(std::ranges::input_range<beman::optional26::optional<int&>>);
@@ -646,7 +647,7 @@ TEST(ViewMaybeTest, ConceptCheckRef) {
     static_assert(std::ranges::random_access_range<beman::optional26::optional<ref>>);
 }
 
-TEST(ViewMaybeTest, BreathingTest) {
+TEST(OptionalTest, BreathingTest) {
     beman::optional26::optional<int> m;
     beman::optional26::optional<int> m1{1};
 
@@ -664,7 +665,7 @@ TEST(ViewMaybeTest, BreathingTest) {
     ASSERT_EQ(*std::begin(d0), 1.0);
 }
 
-TEST(ViewMaybeTest, BreathingTestRef) {
+TEST(OptionalTest, BreathingTestRef) {
     beman::optional26::optional<int&> m;
 
     int                               one = 1;
@@ -683,7 +684,7 @@ TEST(ViewMaybeTest, BreathingTestRef) {
     ASSERT_EQ(*std::begin(d0), 1.0);
 }
 
-TEST(ViewMaybe, CompTest) {
+TEST(OptionalTest, CompTest) {
     beman::optional26::optional<int> m;
     beman::optional26::optional<int> m0{0};
     beman::optional26::optional<int> m1{1};
@@ -703,7 +704,7 @@ TEST(ViewMaybe, CompTest) {
     ASSERT_TRUE(m1 <= m1a);
 }
 
-TEST(ViewMaybe, CompTestRef) {
+TEST(OptionalTest, CompTestRef) {
     beman::optional26::optional<int&> m;
     int                               zero  = 0;
     int                               one   = 1;
@@ -743,7 +744,7 @@ inline constexpr auto yield_if = []<class T>(bool b, T x) {
     return b ? beman::optional26::optional<T>{std::move(x)} : beman::optional26::nullopt;
 };
 
-TEST(ViewMaybeTest, PythTripleTest) {
+TEST(OptionalTest, PythTripleTest) {
     using std::views::iota;
     auto triples = and_then(iota(1), [](int z) {
         return and_then(iota(1, z + 1), [=](int x) {
@@ -757,7 +758,7 @@ TEST(ViewMaybeTest, PythTripleTest) {
 
 using namespace beman;
 
-TEST(ViewMaybeTest, ValueBase) {
+TEST(OptionalTest, ValueBase) {
     int                              i = 7;
     beman::optional26::optional<int> v1{};
 
@@ -769,7 +770,7 @@ TEST(ViewMaybeTest, ValueBase) {
         ASSERT_EQ(i, 7);
 }
 
-TEST(ViewMaybeTest, RefWrapper) {
+TEST(OptionalTest, RefWrapper) {
     int i = 7;
 
     beman::optional26::optional<int> v2{std::ref(i)};
@@ -778,7 +779,7 @@ TEST(ViewMaybeTest, RefWrapper) {
         ASSERT_EQ(i, 7);
 }
 
-TEST(ViewMaybeTest, ValueNonDefaultConstruct) {
+TEST(OptionalTest, ValueNonDefaultConstruct) {
     using beman::optional26::tests::int_ctor;
     int_ctor                              i = 7;
     beman::optional26::optional<int_ctor> v1{};
@@ -787,7 +788,7 @@ TEST(ViewMaybeTest, ValueNonDefaultConstruct) {
     std::ignore = v2;
 }
 
-TEST(ViewMaybeTest, RefBase) {
+TEST(OptionalTest, RefBase) {
     int                               i = 7;
     beman::optional26::optional<int&> v1{};
     // ASSERT_TRUE(v1.size() == 0);
@@ -820,3 +821,25 @@ TEST(ViewMaybeTest, RefBase) {
     }
     ASSERT_EQ(s, 9);
 }
+
+TEST(OptionalTest, HashTest) {
+    beman::optional26::optional<int> o1 = beman::optional26::nullopt;
+    beman::optional26::optional<int> o2 = beman::optional26::nullopt;
+    beman::optional26::optional<int> o3 = 42;
+    beman::optional26::optional<int> o4 = 42;
+
+    auto h1 = std::hash<beman::optional26::optional<int>>{}(o1);
+    auto h2 = std::hash<beman::optional26::optional<int>>{}(o2);
+    auto h3 = std::hash<beman::optional26::optional<int>>{}(o3);
+    auto h4 = std::hash<beman::optional26::optional<int>>{}(o4);
+
+    EXPECT_EQ(h1, h2);
+    EXPECT_EQ(h3, h4);
+    EXPECT_NE(h1, h3);
+
+    for(int i : std::views::iota(0, 1000)) {
+        auto h1 = std::hash<beman::optional26::optional<int>>{}(i);
+        auto h2 = std::hash<int>{}(i);
+        EXPECT_EQ(h1, h2);
+    }
+}