Add default hash for std::pair and std::tuple... slight code reorganization.

README.md

@@ -107,7 +107,7 @@ The full types with template parameters can be found in the [parallel_hashmap/ph
 
 ## Changes to Abseil's hashmaps
 
-- The default hash framework is std::hash, not absl::Hash. However, if you prefer the default to be the Abseil hash framework, include the Abseil headers before `phmap.h` and define the preprocessor macro `PHMAP_USE_ABSL_HASHEQ`.
+- The default hash framework is std::hash, not absl::Hash. However, if you prefer the default to be the Abseil hash framework, include the Abseil headers before `phmap.h` and define the preprocessor macro `PHMAP_USE_ABSL_HASH`.
 
 - The `erase(iterator)` and `erase(const_iterator)` both return an iterator to the element following the removed element, as does the std::unordered_map. A non-standard `void _erase(iterator)` is provided in case the return value is not needed.
 

parallel_hashmap/phmap.h

@@ -47,9 +47,9 @@
 #include <cassert>
 #include <atomic>
 
+#include "phmap_fwd_decl.h"
 #include "phmap_utils.h"
 #include "phmap_base.h"
-#include "phmap_fwd_decl.h"
 
 #if PHMAP_HAVE_STD_STRING_VIEW
     #include <string_view>
@@ -4047,6 +4047,7 @@ struct HashEq<std::wstring_view> : StringHashEqT<wchar_t> {};
 #endif
 
 // Supports heterogeneous lookup for pointers and smart pointers.
+// -------------------------------------------------------------
 template <class T>
 struct HashEq<T*> 
 {
@@ -4068,6 +4069,7 @@ struct HashEq<T*>
 
 private:
     static const T* ToPtr(const T* ptr) { return ptr; }
+
     template <class U, class D>
     static const T* ToPtr(const std::unique_ptr<U, D>& ptr) {
         return ptr.get();

parallel_hashmap/phmap_fwd_decl.h

@@ -14,9 +14,18 @@
 #include <memory>
 #include <utility>
 
+#if defined(PHMAP_USE_ABSL_HASH)
+    namespace absl { template <class T> struct Hash; };
+#endif
+
 namespace phmap {
 
+#if defined(PHMAP_USE_ABSL_HASH)
+    template <class T> using Hash = absl::Hash<T>;
+#else
     template <class T> struct Hash;
+#endif
+
     template <class T> struct EqualTo;
     template <class T> using Allocator      = typename std::allocator<T>;
     template<class T1, class T2> using Pair = typename std::pair<T1, T2>;
@@ -29,13 +38,8 @@ namespace phmap {
         template <class T, class E = void>
         struct HashEq 
         {
-#if defined(PHMAP_USE_ABSL_HASHEQ)
-            using Hash = absl::Hash<T>;
-            using Eq   = phmap::EqualTo<T>;
-#else
             using Hash = phmap::Hash<T>;
             using Eq   = phmap::EqualTo<T>;
-#endif
         };
 
         template <class T>

parallel_hashmap/phmap_utils.h

@@ -23,6 +23,7 @@
 
 #include <cstdint>
 #include <functional>
+#include <tuple>
 #include "phmap_bits.h"
 
 namespace phmap
@@ -123,6 +124,10 @@ public:
     static constexpr bool value = std::is_same<decltype(test<T>(0)), yes>::value;
 };
 
+#if defined(PHMAP_USE_ABSL_HASH) && !defined(phmap_fwd_decl_h_guard_)
+    namespace absl { template <class T> struct Hash; };
+    template <class T> using Hash = absl::Hash<T>;
+#else
 // ---------------------------------------------------------------
 //               phmap::Hash
 // ---------------------------------------------------------------
@@ -264,6 +269,8 @@ struct Hash<double> : public phmap_unary_function<double, size_t>
     }
 };
 
+#endif
+
 template <class H, int sz> struct Combiner
 {
     H operator()(H seed, size_t value);
@@ -285,7 +292,7 @@ template <class H> struct Combiner<H, 8>
     }
 };
 
-
+// define HashState to combine member hashes... see example below
 // -----------------------------------------------------------------------------
 template <typename H>
 class HashStateBase {
@@ -301,11 +308,51 @@ template <typename T, typename... Ts>
 H HashStateBase<H>::combine(H seed, const T& v, const Ts&... vs)
 {
     return HashStateBase<H>::combine(Combiner<H, sizeof(H)>()(
-                                         seed, phmap::Hash<T>()(v)),  vs...);
+                                         seed, phmap::Hash<T>()(v)), 
+                                     vs...);
 }
 
 using HashState = HashStateBase<size_t>;
 
+// -----------------------------------------------------------------------------
+
+#if !defined(PHMAP_USE_ABSL_HASH)
+
+// define Hash for std::pair
+// -------------------------
+template<class T1, class T2> 
+struct Hash<std::pair<T1, T2>> {
+    size_t operator()(std::pair<T1, T2> const& p) const noexcept {
+        return phmap::HashState().combine(0, p.first, p.second);
+    }
+};
+
+// define Hash for std::tuple
+// --------------------------
+template<class... T> 
+struct Hash<std::tuple<T...>> {
+    size_t operator()(std::tuple<T...> const& t) const noexcept {
+        return _hash_helper(t);
+    }
+
+private:
+    template<size_t I = 0, class ...P>
+        typename std::enable_if<I == sizeof...(P), size_t>::type
+        _hash_helper(const std::tuple<P...> &) const noexcept { return 0; }
+
+    template<size_t I = 0, class ...P>
+    typename std::enable_if<I < sizeof...(P), size_t>::type
+    _hash_helper(const std::tuple<P...> &t) const noexcept {
+        const auto &el = std::get<I>(t);
+        using el_type = std::remove_cv<std::remove_reference<decltype(el)>::type>::type;
+        return phmap::Hash<el_type>()(el) + _hash_helper<I + 1>(t);
+    }
+};
+
+
+#endif
+
+
 }  // namespace phmap