voice interface and type checks

synth/ivoice.h

@@ -0,0 +1,25 @@
+#pragma once
+
+namespace trnr {
+struct ivoice {
+    virtual ~ivoice() = default;
+    virtual float process_sample() = 0;
+    virtual bool is_busy() = 0;
+    virtual void set_samplerate(double samplerate) = 0;
+    virtual void note_on(int _note, float _velocity) = 0;
+    virtual void note_off() = 0;
+    virtual void modulate_pitch(float _pitch) = 0;
+};
+
+// check if a template derives from ivoice
+template <class derived>
+struct is_convertible {
+    template <class T>
+    static char test(T*);
+
+    template <class T>
+    static double test(...);
+
+    static const bool value = sizeof(test<ivoice>(static_cast<derived*>(0))) == 1;
+};
+}

synth/midi_synth.h

@@ -1,18 +1,22 @@
 #pragma once
 #include <memory>
 #include <vector>
+#include "ivoice.h"
 #include "midi_event.h"
 #include "voice_allocator.h"
 
 namespace trnr {
 
 // a generic midi synth base class with sample accurate event handling.
+// the templated type t_voice must derive from ivoice
 template <typename t_voice>
 class midi_synth : public voice_allocator<t_voice> {
 public:
     midi_synth(int _n_voices)
         : m_voices_active { false }
     {
+        // checks whether template derives from ivoice
+        typedef t_voice assert_at_compile_time[is_convertible<t_voice>::value ? 1 : -1];
     }
 
     void set_samplerate_blocksize(double _samplerate, int _block_size)

synth/tx_voice.h

@@ -2,11 +2,12 @@
 #include "tx_sineosc.h"
 #include "tx_envelope.h"
 #include "tx_operator.h"
+#include "ivoice.h"
 #include "../util/audio_math.h"
 
 namespace trnr {
 
-class tx_voice {
+class tx_voice : public ivoice {
 public:
     tx_voice() 
         : algorithm { 0 }
@@ -32,23 +33,23 @@ public:
     tx_operator op2;
     tx_operator op3;
 
-    void note_on(int _note, float _velocity) {
+    void note_on(int _note, float _velocity) override {
         this->gate = true;
         this->trigger = true;
         midi_note = _note;
         velocity = _velocity;
     }
 
-    void note_off() {
+    void note_off() override {
         this->gate = false;
     }
 
     // modulates the pitch in semitones
-    void modulate_pitch(float pitch) {
-        this->pitch_mod = pitch;
+    void modulate_pitch(float _pitch) override {
+        this->pitch_mod = _pitch;
     }
 
-    float process_sample() {
+    float process_sample() override {
         float pitch_env_signal = pitch_env.process_sample(gate, trigger) * pitch_env_amt;
         float pitched_freq = midi_to_frequency(midi_note + pitch_mod + additional_pitch_mod) + pitch_env_signal;
 
@@ -79,9 +80,9 @@ public:
         return redux(output, bit_resolution);
     }
 
-    bool is_busy() { return gate || op1.envelope.is_busy() || op2.envelope.is_busy() || op3.envelope.is_busy(); }
+    bool is_busy() override { return gate || op1.envelope.is_busy() || op2.envelope.is_busy() || op3.envelope.is_busy(); }
 
-    void set_samplerate(double samplerate) {
+    void set_samplerate(double samplerate) override {
         pitch_env.set_samplerate(samplerate);
         feedback_osc.set_samplerate(samplerate);
         op1.set_samplerate(samplerate);

synth/voice_allocator.h

@@ -1,5 +1,6 @@
 #pragma once
 #include "midi_event.h"
+#include "ivoice.h"
 #include <vector>
 
 namespace trnr {
@@ -12,6 +13,8 @@ public:
     voice_allocator()
         : voices(8, t_voice())
     {
+        // checks whether template derives from ivoice
+        typedef t_voice assert_at_compile_time[is_convertible<t_voice>::value ? 1 : -1];
     }
 
     void set_voice_count(const int& voice_count)