Support for std::hash

Author: gershnik

CHANGELOG.md

@@ -7,7 +7,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 
 ### Added
 - Support for `std::format` (if available). Instances of `intrusive_shared_ptr` can be passed to `std::format`
-  and will be printed like a `void *`. 
+  and will be printed like a `void *`.
+- Support for `std::hash<intrusive_shared_ptr>`. 
 - `get_inout_param()` method. This provides the same functionality as `std::inout_ptr` but is available for pre-C++23 compilation.
 
 ### Changed

doc/intrusive_shared_ptr.md

@@ -85,7 +85,8 @@ using traits_type = Traits;
   any traits as well as raw pointers and nullptr.
 - Comparisons: `<`, `<=`, `>=`, `>`. All `noexcept`. On C++20 these are replaced by `<=>`. Work between `intrusive_shared_ptr` of compatible types and
   any traits as well as raw pointers.
-- Namespace method: `template<class Char> friend std::basic_ostream<Char> & operator<<(std::basic_ostream<Char> & str, const intrusive_shared_ptr<T, Traits> & ptr)` (ADL only) outputs the stored pointer value to a stream
+- Hash code: `constexpr size_t hash_value(const intrusive_shared_ptr<T, Traits> & ptr) noexcept`. 
+- Stream output: `template<class Char> friend std::basic_ostream<Char> & operator<<(std::basic_ostream<Char> & str, const intrusive_shared_ptr<T, Traits> & ptr)` (ADL only) outputs the stored pointer value to a stream
 
 - `Dest intrusive_const_cast<Dest>(intrusive_shared_ptr src) noexcept`. Performs an equivalent of `const_cast` on passed argument. The destination type needs to be a valid `intrusive_shared_ptr` type whose underlying type is convertible from source's via `const_cast`.
 - `Dest intrusive_static_cast<Dest>(intrusive_shared_ptr src) noexcept`. Performs an equivalent of `static_cast` on passed argument. The destination type needs to be a valid `intrusive_shared_ptr` type whose underlying type is convertible from source's via `static_cast`.
@@ -96,6 +97,7 @@ using traits_type = Traits;
 - `std::out_ptr_t<intrusive_shared_ptr>` and `std::inout_ptr_t<intrusive_shared_ptr>`. Provide support for using
   `std::out_ptr` and `std::inout_ptr` with `intrusive_shared_ptr`
 - `std::formatter<intrusive_shared_ptr>`. Provides support for using `std::format` with `intrusive_shared_ptr` instances
+- `std::hash<intrusive_shared_ptr>`
 
 ## Class std::atomic&lt;isptr::intrusive_shared_ptr&gt;
 

inc/intrusive_shared_ptr/common.h

@@ -37,8 +37,6 @@
 #endif
 
 #if __cpp_lib_out_ptr >= 202106L
-    
-    #include <memory>
 
     #define ISPTR_SUPPORT_OUT_PTR 1
 

inc/intrusive_shared_ptr/intrusive_shared_ptr.h

@@ -14,6 +14,7 @@
 #include <type_traits>
 #include <ostream>
 #include <atomic>
+#include <memory>
 
 
 namespace isptr
@@ -334,6 +335,9 @@ namespace isptr
         template<class Char>
         friend std::basic_ostream<Char> & operator<<(std::basic_ostream<Char> & str, const intrusive_shared_ptr<T, Traits> & ptr)
             { return str << ptr.m_p; }
+
+        friend constexpr size_t hash_value(const intrusive_shared_ptr<T, Traits> & ptr) noexcept 
+            { return std::hash<T *>()(ptr.m_p); }
 
     private:
         constexpr intrusive_shared_ptr(T * ptr) noexcept :
@@ -557,6 +561,14 @@ namespace std
             { return formatter<void *, CharT>::format(ptr.get(), ctx); }
     };
 #endif
+
+    ISPTR_EXPORTED
+    template<class T, class Traits>
+    struct hash<::isptr::intrusive_shared_ptr<T, Traits>> 
+    {
+        constexpr size_t operator()(const ::isptr::intrusive_shared_ptr<T, Traits> & ptr) const noexcept 
+            { return hash_value(ptr); }
+    };
 }
 
 #undef ISPTR_TRIVIAL_ABI

modules/isptr.cppm

@@ -71,7 +71,6 @@ export module isptr;
 #endif
 
 #if __cpp_lib_out_ptr >= 202106L
-    
 
     #define ISPTR_SUPPORT_OUT_PTR 1
 
@@ -447,6 +446,9 @@ namespace isptr
         template<class Char>
         friend std::basic_ostream<Char> & operator<<(std::basic_ostream<Char> & str, const intrusive_shared_ptr<T, Traits> & ptr)
             { return str << ptr.m_p; }
+
+        friend constexpr size_t hash_value(const intrusive_shared_ptr<T, Traits> & ptr) noexcept 
+            { return std::hash<T *>()(ptr.m_p); }
 
     private:
         constexpr intrusive_shared_ptr(T * ptr) noexcept :
@@ -670,6 +672,14 @@ namespace std
             { return formatter<void *, CharT>::format(ptr.get(), ctx); }
     };
 #endif
+
+    ISPTR_EXPORTED
+    template<class T, class Traits>
+    struct hash<::isptr::intrusive_shared_ptr<T, Traits>> 
+    {
+        constexpr size_t operator()(const ::isptr::intrusive_shared_ptr<T, Traits> & ptr) const noexcept 
+            { return hash_value(ptr); }
+    };
 }
 
 #undef ISPTR_TRIVIAL_ABI

test/test_general.cpp

@@ -562,4 +562,13 @@ TEST_CASE( "Member pointer" ) {
     CHECK(x == 1);
 }
 
+TEST_CASE( "Hash code" ) {
+
+    instrumented_counted<> object;
+    auto ptr = mock_noref(&object);
+    
+    CHECK(std::hash<decltype(ptr)>()(ptr) == std::hash<instrumented_counted<> *>()(&object));
+    CHECK(std::hash<decltype(ptr)>()(ptr) == hash_value(ptr));
+}
+
 }