Implement the identifier in a better and more safe way

src/sfizz/NumericId.h

@@ -0,0 +1,31 @@
+// SPDX-License-Identifier: BSD-2-Clause
+
+// This code is part of the sfizz library and is licensed under a BSD 2-clause
+// license. You should have receive a LICENSE.md file along with the code.
+// If not, contact the sfizz maintainers at https://github.com/sfztools/sfizz
+
+#pragma once
+
+/**
+ * @brief Numeric identifier
+ *
+ * It is a generic numeric identifier. The template wrapper serves to enforce a
+ * stronger compile-time check, such that one kind of identifier can't be
+ * mistaken for another kind, or for an unrelated integer such as an index.
+ */
+template <class T>
+struct NumericId {
+    constexpr NumericId() = default;
+
+    explicit constexpr NumericId(int number)
+        : number(number)
+    {
+    }
+
+    constexpr bool valid() const noexcept
+    {
+        return number != -1;
+    }
+
+    const int number = -1;
+};

src/sfizz/Region.h

@@ -16,6 +16,7 @@
 #include "AudioBuffer.h"
 #include "MidiState.h"
 #include "FileId.h"
+#include "NumericId.h"
 #include "absl/types/optional.h"
 #include <bitset>
 #include <string>
@@ -36,7 +37,7 @@ namespace sfz {
  */
 struct Region {
     Region(int regionNumber, const MidiState& midiState, absl::string_view defaultPath = "")
-    : regionNumber(regionNumber), midiState(midiState), defaultPath(std::move(defaultPath))
+    : id{regionNumber}, midiState(midiState), defaultPath(std::move(defaultPath))
     {
         ccSwitched.set();
 
@@ -49,9 +50,9 @@ struct Region {
     /**
      * @brief Get the number which identifies this region
      */
-    int getIdNumber() const noexcept
+    NumericId<Region> getId() const noexcept
     {
-        return regionNumber;
+        return id;
     }
 
     /**
@@ -246,7 +247,7 @@ struct Region {
      */
     float getGainToEffectBus(unsigned number) const noexcept;
 
-    const int regionNumber { -1 };
+    const NumericId<Region> id;
 
     // Sound source: sample playback
     FileId sampleId {}; // Sample

src/sfizz/Synth.cpp

@@ -44,11 +44,11 @@ sfz::Synth::~Synth()
     resources.filePool.emptyFileLoadingQueues();
 }
 
-void sfz::Synth::onVoiceStateChanged(int idNumber, Voice::State state)
+void sfz::Synth::onVoiceStateChanged(NumericId<Voice> id, Voice::State state)
 {
-    (void)idNumber;
+    (void)id;
     (void)state;
-    DBG("Voice " << idNumber << ": state " << static_cast<int>(state));
+    DBG("Voice " << id.number << ": state " << static_cast<int>(state));
 }
 
 void sfz::Synth::onParseFullBlock(const std::string& header, const std::vector<Opcode>& members)

src/sfizz/Synth.h

@@ -497,7 +497,7 @@ protected:
     /**
      * @brief The voice callback which is called during a change of state.
      */
-    void onVoiceStateChanged(int idNumber, Voice::State state) override;
+    void onVoiceStateChanged(NumericId<Voice> idNumber, Voice::State state) override;
 
 protected:
     /**

src/sfizz/Voice.cpp

@@ -15,7 +15,7 @@
 #include "absl/algorithm/container.h"
 
 sfz::Voice::Voice(int voiceNumber, sfz::Resources& resources)
-: voiceNumber(voiceNumber), stateListener(nullptr), resources(resources)
+: id{voiceNumber}, stateListener(nullptr), resources(resources)
 {
     filters.reserve(config::filtersPerVoice);
     equalizers.reserve(config::eqsPerVoice);
@@ -773,6 +773,6 @@ void sfz::Voice::switchState(State s)
     if (s != state) {
         state = s;
         if (stateListener)
-            stateListener->onVoiceStateChanged(voiceNumber, s);
+            stateListener->onVoiceStateChanged(id, s);
     }
 }

src/sfizz/Voice.h

@@ -14,6 +14,7 @@
 #include "AudioSpan.h"
 #include "LeakDetector.h"
 #include "OnePoleFilter.h"
+#include "NumericId.h"
 #include "absl/types/span.h"
 #include <memory>
 #include <random>
@@ -41,12 +42,13 @@ public:
         NoteOff,
         CC
     };
+
     /**
-     * @brief Get the number which identifies this voice
+     * @brief Get the unique identifier of this voice in a synth
      */
-    int getIdNumber() const noexcept
+    NumericId<Voice> getId() const noexcept
     {
-        return voiceNumber;
+        return id;
     }
 
     enum class State {
@@ -56,7 +58,7 @@ public:
 
     class StateListener {
     public:
-        virtual void onVoiceStateChanged(int /*idNumber*/, State /*state*/) {}
+        virtual void onVoiceStateChanged(NumericId<Voice> /*id*/, State /*state*/) {}
     };
 
     /**
@@ -299,7 +301,7 @@ private:
      */
     void switchState(State s);
 
-    const int voiceNumber { -1 };
+    const NumericId<Voice> id;
     StateListener* stateListener = nullptr;
 
     Region* region { nullptr };