From f2cbed07fe7bcc5646b3424885587c20e35c7fa8 Mon Sep 17 00:00:00 2001
From: Davide Faconti <davide.faconti@gmail.com>
Date: Thu, 1 Feb 2024 14:32:04 +0100
Subject: [PATCH] add std::hash<DataTamer::RegistrationID>

---
 data_tamer_cpp/include/data_tamer/types.hpp | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/data_tamer_cpp/include/data_tamer/types.hpp b/data_tamer_cpp/include/data_tamer/types.hpp
index ffdcc0f..7da8dde 100644
--- a/data_tamer_cpp/include/data_tamer/types.hpp
+++ b/data_tamer_cpp/include/data_tamer/types.hpp
@@ -148,3 +148,18 @@ std::string ToStr(const Schema& schema);
 [[nodiscard]] uint64_t AddFieldToHash(const TypeField& field, uint64_t hash);
 
 }   // namespace DataTamer
+
+
+template <>
+struct std::hash<DataTamer::RegistrationID>
+{
+  std::size_t operator()( const DataTamer::RegistrationID& id ) const
+  {
+    // Compute individual hash values for first, second and third
+    // http://stackoverflow.com/a/1646913/126995
+    std::size_t res = 17;
+    res = res * 31 + hash<size_t>()( id.first_index );
+    res = res * 31 + hash<size_t>()( id.fields_count );
+    return res;
+  }
+};