Create FairTypes.h

Created `namespace FairRoot`
with `struct EntryID {size_t fId;}`.

Should replace PR #1405.

fairroot/base/CMakeLists.txt

@@ -82,6 +82,10 @@ endif()
 
 fair_change_extensions_if_exists(.cxx .h FILES "${sources}" OUTVAR headers)
 
+list(APPEND headers
+  steer/FairTypes.h
+)
+
 add_library(${target} SHARED ${sources} ${headers})
 fairroot_library_settings(${target})
 

fairroot/base/steer/FairTypes.h

@@ -0,0 +1,106 @@
+/********************************************************************************
+ * Copyright (C) 2014-2023 GSI Helmholtzzentrum fuer Schwerionenforschung GmbH  *
+ *                                                                              *
+ *              This software is distributed under the terms of the             *
+ *              GNU Lesser General Public Licence (LGPL) version 3,             *
+ *                  copied verbatim in the file "LICENSE"                       *
+ ********************************************************************************/
+/*
+ * FairTypes.h
+ *
+ *  Created on: May 16, 2023
+ *      Author: R.Karabowicz
+ */
+
+#ifndef FAIR_TYPES_H_
+#define FAIR_TYPES_H_
+
+#include <iostream>
+#include <limits>
+
+/**
+ * \brief Main namespace for FairRoot classes / types
+ *
+ * All new public classes and types of FairRoot will be in this namespace.
+ * Note: Nost classes are still in no namespace.
+ */
+namespace FairRoot {
+/**
+ * \brief Ordinal identification number of entry in IO stream
+ *
+ * Data stored in ROOT trees are gropued into entries, 
+ * essentially equivalent to HEP events
+ */
+struct EntryID
+{
+    using underlying_type = size_t;
+
+    static const EntryID None;
+
+    EntryID(underlying_type value)
+        : fId(value)
+    {}
+
+    EntryID() = default;
+
+    operator underlying_type() const { return fId; }
+
+    friend auto operator<<(std::ostream& os, EntryID id) -> std::ostream&
+    {
+        if (id == None) {
+            return os << "<No Entry>";
+        }
+        return os << static_cast<underlying_type>(id);
+    }
+
+    auto operator++()
+    {
+        if (fId != None) {
+            ++fId;
+        }
+        return *this;
+    }
+    auto operator++(int)
+    {
+        auto temp = *this;
+        if (fId != None) {
+            ++fId;
+        }
+        return temp;
+    }
+
+    auto operator--()
+    {
+        if (fId != None) {
+            --fId;
+        }
+        return *this;
+    }
+    auto operator--(int)
+    {
+        auto temp = *this;
+        if (fId != None) {
+            --fId;
+        }
+        return temp;
+    }
+    auto operator+=(const EntryID& rhs)
+    {
+        fId += rhs.fId;
+        return *this;
+    }
+    auto operator-=(const EntryID& rhs)
+    {
+        fId -= rhs.fId;
+        return *this;
+    }
+
+  private:
+    underlying_type fId{std::numeric_limits<underlying_type>::max()};
+};
+
+/// \sa https://stackoverflow.com/questions/29432283/c-static-constexpr-field-with-incomplete-type/50295183#50295183
+inline constexpr const EntryID EntryID::None{};
+}   // namespace FairRoot
+
+#endif   // FAIR_TYPES_H_