kstd: implement string hash support

2 files changed, 56 insertions, 0 deletions

diff --git a/libs/kstd/kstd/bits/basic_string.hpp b/libs/kstd/kstd/bits/basic_string.hpp
index 212aa8ac..4d690ac3 100644
--- a/libs/kstd/kstd/bits/basic_string.hpp
+++ b/libs/kstd/kstd/bits/basic_string.hpp
@@ -10,6 +10,7 @@
 #include <array>
 #include <compare>
 #include <cstddef>
+#include <functional>
 #include <initializer_list>
 #include <iterator>
 #include <limits>
@@ -1546,4 +1547,24 @@ namespace kstd
 
 }  // namespace kstd
 
+//! A specialization of std::hash for kstd::string.
+//!
+//! This specialization allows for the use of kstd::string in hashed containers.
+//!
+//! @note Under the hood, this specialization delegates to the specialization for std::string_view. This saves
+//! implementation work and automatically guarantees that the hash for a kstd::string with some contents X is equal to
+//! the hash of a std::string_view of the same X. This is a standard requirement for the specialization for std::string,
+//! so providing the same for kstd::string yields the same interoperability.
+template<typename Allocator>
+struct std::hash<kstd::basic_string<char, kstd::char_traits<char>, Allocator>>
+{
+  constexpr auto static implementation = std::hash<std::string_view>{};
+
+  constexpr auto operator()(kstd::basic_string<char, kstd::char_traits<char>, Allocator> string) const noexcept
+      -> std::size_t
+  {
+    return implementation(string);
+  };
+};
+
 #endif
diff --git a/libs/kstd/kstd/string.test.cpp b/libs/kstd/kstd/string.test.cpp
index 3fbf6c0c..2de8b513 100644
--- a/libs/kstd/kstd/string.test.cpp
+++ b/libs/kstd/kstd/string.test.cpp
@@ -8,9 +8,11 @@
 #include <algorithm>
 #include <cstring>
 #include <forward_list>
+#include <functional>
 #include <iterator>
 #include <memory>
 #include <sstream>
+#include <string>
 #include <string_view>
 #include <type_traits>
 #include <utility>
@@ -2942,3 +2944,36 @@ SCENARIO("String iteration", "[string]")
     }
   }
 }
+
+SCENARIO("String STL integration", "[string]")
+{
+  GIVEN("An empty string")
+  {
+    auto s = kstd::string{""};
+
+    WHEN("hashing the string")
+    {
+      auto hash_result = std::hash<kstd::string>{}(s);
+
+      THEN("the result is equal to hashing an empty std::string")
+      {
+        REQUIRE(hash_result == std::hash<std::string>{}(""));
+      }
+    }
+  }
+
+  GIVEN("A non-empty string")
+  {
+    auto s = kstd::string{"abcd"};
+
+    WHEN("hashing the string")
+    {
+      auto hash_result = std::hash<kstd::string>{}(s);
+
+      THEN("the result is equal to hashing the same std::string")
+      {
+        REQUIRE(hash_result == std::hash<std::string>{}("abcd"));
+      }
+    }
+  }
+}