[NFC] Add a generic hash implementation for tuples (#5162)

We already provided a specialization of `std::hash` for arbitrary pairs, so add
one for `std::tuple` as well. Use the new specialization where we were
previously using nested pairs just to be able to use the pair specialization.

1 files changed, 18 insertions, 0 deletions

diff --git a/src/support/hash.h b/src/support/hash.h
index fb0e710a5..fc8b358f2 100644
--- a/src/support/hash.h
+++ b/src/support/hash.h
@@ -61,6 +61,24 @@ template<typename T1, typename T2> struct hash<pair<T1, T2>> {
   }
 };
 
+// And hashing tuples is useful, too.
+template<typename T, typename... Ts> struct hash<tuple<T, Ts...>> {
+private:
+  template<size_t... I>
+  static void rehash(const tuple<T, Ts...>& tup,
+                     size_t& digest,
+                     std::index_sequence<I...>) {
+    (wasm::rehash(digest, std::get<1 + I>(tup)), ...);
+  }
+
+public:
+  size_t operator()(const tuple<T, Ts...>& tup) const {
+    auto digest = wasm::hash(std::get<0>(tup));
+    rehash(tup, digest, std::index_sequence_for<Ts...>{});
+    return digest;
+  }
+};
+
 } // namespace std
 
 #endif // wasm_support_hash_h