10 files changed, 199 insertions, 297 deletions

diff --git a/src/mixer/MixerControl.cxx b/src/mixer/MixerControl.cxx
index 2c030cdfd..e7b6e8395 100644
--- a/src/mixer/MixerControl.cxx
+++ b/src/mixer/MixerControl.cxx
@@ -46,7 +46,7 @@ mixer_free(Mixer *mixer)
 	   this point (see mixer_auto_close()) */
 	mixer_close(mixer);
 
-	mixer->plugin.finish(mixer);
+	delete mixer;
 }
 
 bool
@@ -58,12 +58,7 @@ mixer_open(Mixer *mixer, Error &error)
 
 	const ScopeLock protect(mixer->mutex);
 
-	if (mixer->open)
-		success = true;
-	else if (mixer->plugin.open == nullptr)
-		success = mixer->open = true;
-	else
-		success = mixer->open = mixer->plugin.open(mixer, error);
+	success = mixer->open || (mixer->open = mixer->Open(error));
 
 	mixer->failed = !success;
 
@@ -76,9 +71,7 @@ mixer_close_internal(Mixer *mixer)
 	assert(mixer != nullptr);
 	assert(mixer->open);
 
-	if (mixer->plugin.close != nullptr)
-		mixer->plugin.close(mixer);
-
+	mixer->Close();
 	mixer->open = false;
 }
 
@@ -128,7 +121,7 @@ mixer_get_volume(Mixer *mixer, Error &error)
 	const ScopeLock protect(mixer->mutex);
 
 	if (mixer->open) {
-		volume = mixer->plugin.get_volume(mixer, error);
+		volume = mixer->GetVolume(error);
 		if (volume < 0 && error.IsDefined())
 			mixer_failed(mixer);
 	} else
@@ -149,6 +142,5 @@ mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
 
 	const ScopeLock protect(mixer->mutex);
 
-	return mixer->open &&
-		mixer->plugin.set_volume(mixer, volume, error);
+	return mixer->open && mixer->SetVolume(volume, error);
 }
diff --git a/src/mixer/MixerInternal.hxx b/src/mixer/MixerInternal.hxx
index 5d1ad1362..2c6282ebb 100644
--- a/src/mixer/MixerInternal.hxx
+++ b/src/mixer/MixerInternal.hxx
@@ -23,6 +23,7 @@
 #include "MixerPlugin.hxx"
 #include "MixerList.hxx"
 #include "thread/Mutex.hxx"
+#include "Compiler.h"
 
 class Mixer {
 public:
@@ -53,9 +54,40 @@ public:
 
 	Mixer(const Mixer &) = delete;
 
+	virtual ~Mixer() {}
+
 	bool IsPlugin(const MixerPlugin &other) const {
 		return &plugin == &other;
 	}
+
+	/**
+	 * Open mixer device
+	 *
+	 * @return true on success, false on error
+	 */
+	virtual bool Open(Error &error) = 0;
+
+	/**
+	 * Close mixer device
+	 */
+	virtual void Close() = 0;
+
+	/**
+	 * Reads the current volume.
+	 *
+	 * @return the current volume (0..100 including) or -1 if
+	 * unavailable or on error (error set, mixer will be closed)
+	 */
+	gcc_pure
+	virtual int GetVolume(Error &error) = 0;
+
+	/**
+	 * Sets the volume.
+	 *
+	 * @param volume the new volume (0..100 including) @return
+	 * true on success, false on error
+	 */
+	virtual bool SetVolume(unsigned volume, Error &error) = 0;
 };
 
 #endif
diff --git a/src/mixer/MixerPlugin.hxx b/src/mixer/MixerPlugin.hxx
index d342ba1a7..27e59accf 100644
--- a/src/mixer/MixerPlugin.hxx
+++ b/src/mixer/MixerPlugin.hxx
@@ -47,46 +47,6 @@ struct MixerPlugin {
 		       Error &error);
 
 	/**
-	 * Finish and free mixer data
-         */
-	void (*finish)(Mixer *data);
-
-	/**
-	 * Open mixer device
-	 *
-	 * @param error_r location to store the error occurring, or
-	 * nullptr to ignore errors
-	 * @return true on success, false on error
-	 */
-	bool (*open)(Mixer *data, Error &error);
-
-	/**
-	 * Close mixer device
-	 */
-	void (*close)(Mixer *data);
-
-	/**
-	 * Reads the current volume.
-	 *
-	 * @param error_r location to store the error occurring, or
-	 * nullptr to ignore errors
-	 * @return the current volume (0..100 including) or -1 if
-	 * unavailable or on error (error set, mixer will be closed)
-	 */
-	int (*get_volume)(Mixer *mixer, Error &error);
-
-	/**
-	 * Sets the volume.
-	 *
-	 * @param error_r location to store the error occurring, or
-	 * nullptr to ignore errors
-	 * @param volume the new volume (0..100 including)
-	 * @return true on success, false on error
-	 */
-	bool (*set_volume)(Mixer *mixer, unsigned volume,
-			   Error &error);
-
-	/**
 	 * If true, then the mixer is automatically opened, even if
 	 * its audio output is not open.  If false, then the mixer is
 	 * disabled as long as its audio output is closed.
diff --git a/src/mixer/plugins/AlsaMixerPlugin.cxx b/src/mixer/plugins/AlsaMixerPlugin.cxx
index 6fb669c54..3a520725f 100644
--- a/src/mixer/plugins/AlsaMixerPlugin.cxx
+++ b/src/mixer/plugins/AlsaMixerPlugin.cxx
@@ -79,13 +79,16 @@ public:
 	AlsaMixer(EventLoop &_event_loop)
 		:Mixer(alsa_mixer_plugin), event_loop(_event_loop) {}
 
+	virtual ~AlsaMixer();
+
 	void Configure(const config_param &param);
 	bool Setup(Error &error);
-	bool Open(Error &error);
-	void Close();
 
-	int GetVolume(Error &error);
-	bool SetVolume(unsigned volume, Error &error);
+	/* virtual methods from class Mixer */
+	virtual bool Open(Error &error) override;
+	virtual void Close() override;
+	virtual int GetVolume(Error &error) override;
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static constexpr Domain alsa_mixer_domain("alsa_mixer");
@@ -174,13 +177,8 @@ alsa_mixer_init(EventLoop &event_loop, gcc_unused void *ao,
 	return am;
 }
 
-static void
-alsa_mixer_finish(Mixer *data)
+AlsaMixer::~AlsaMixer()
 {
-	AlsaMixer *am = (AlsaMixer *)data;
-
-	delete am;
-
 	/* free libasound's config cache */
 	snd_config_update_free_global();
 }
@@ -267,14 +265,6 @@ AlsaMixer::Open(Error &error)
 	return true;
 }
 
-static bool
-alsa_mixer_open(Mixer *data, Error &error)
-{
-	AlsaMixer *am = (AlsaMixer *)data;
-
-	return am->Open(error);
-}
-
 inline void
 AlsaMixer::Close()
 {
@@ -286,13 +276,6 @@ AlsaMixer::Close()
 	snd_mixer_close(handle);
 }
 
-static void
-alsa_mixer_close(Mixer *data)
-{
-	AlsaMixer *am = (AlsaMixer *)data;
-	am->Close();
-}
-
 inline int
 AlsaMixer::GetVolume(Error &error)
 {
@@ -332,13 +315,6 @@ AlsaMixer::GetVolume(Error &error)
 	return ret;
 }
 
-static int
-alsa_mixer_get_volume(Mixer *mixer, Error &error)
-{
-	AlsaMixer *am = (AlsaMixer *)mixer;
-	return am->GetVolume(error);
-}
-
 inline bool
 AlsaMixer::SetVolume(unsigned volume, Error &error)
 {
@@ -367,19 +343,7 @@ AlsaMixer::SetVolume(unsigned volume, Error &error)
 	return true;
 }
 
-static bool
-alsa_mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
-{
-	AlsaMixer *am = (AlsaMixer *)mixer;
-	return am->SetVolume(volume, error);
-}
-
 const MixerPlugin alsa_mixer_plugin = {
 	alsa_mixer_init,
-	alsa_mixer_finish,
-	alsa_mixer_open,
-	alsa_mixer_close,
-	alsa_mixer_get_volume,
-	alsa_mixer_set_volume,
 	true,
 };
diff --git a/src/mixer/plugins/OssMixerPlugin.cxx b/src/mixer/plugins/OssMixerPlugin.cxx
index 7e8d96ca8..fc86f292e 100644
--- a/src/mixer/plugins/OssMixerPlugin.cxx
+++ b/src/mixer/plugins/OssMixerPlugin.cxx
@@ -41,7 +41,7 @@
 
 #define VOLUME_MIXER_OSS_DEFAULT		"/dev/mixer"
 
-class OssMixer : public Mixer {
+class OssMixer final : public Mixer {
 	const char *device;
 	const char *control;
 
@@ -52,11 +52,12 @@ public:
 	OssMixer():Mixer(oss_mixer_plugin) {}
 
 	bool Configure(const config_param &param, Error &error);
-	bool Open(Error &error);
-	void Close();
 
-	int GetVolume(Error &error);
-	bool SetVolume(unsigned volume, Error &error);
+	/* virtual methods from class Mixer */
+	virtual bool Open(Error &error) override;
+	virtual void Close() override;
+	virtual int GetVolume(Error &error) override;
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static constexpr Domain oss_mixer_domain("oss_mixer");
@@ -110,14 +111,6 @@ oss_mixer_init(gcc_unused EventLoop &event_loop, gcc_unused void *ao,
 	return om;
 }
 
-static void
-oss_mixer_finish(Mixer *data)
-{
-	OssMixer *om = (OssMixer *) data;
-
-	delete om;
-}
-
 void
 OssMixer::Close()
 {
@@ -126,14 +119,7 @@ OssMixer::Close()
 	close(device_fd);
 }
 
-static void
-oss_mixer_close(Mixer *data)
-{
-	OssMixer *om = (OssMixer *) data;
-	om->Close();
-}
-
-inline bool
+bool
 OssMixer::Open(Error &error)
 {
 	device_fd = open_cloexec(device, O_RDONLY, 0);
@@ -163,15 +149,7 @@ OssMixer::Open(Error &error)
 	return true;
 }
 
-static bool
-oss_mixer_open(Mixer *data, Error &error)
-{
-	OssMixer *om = (OssMixer *) data;
-
-	return om->Open(error);
-}
-
-inline int
+int
 OssMixer::GetVolume(Error &error)
 {
 	int left, right, level;
@@ -197,14 +175,7 @@ OssMixer::GetVolume(Error &error)
 	return left;
 }
 
-static int
-oss_mixer_get_volume(Mixer *mixer, Error &error)
-{
-	OssMixer *om = (OssMixer *)mixer;
-	return om->GetVolume(error);
-}
-
-inline bool
+bool
 OssMixer::SetVolume(unsigned volume, Error &error)
 {
 	int level;
@@ -224,19 +195,7 @@ OssMixer::SetVolume(unsigned volume, Error &error)
 	return true;
 }
 
-static bool
-oss_mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
-{
-	OssMixer *om = (OssMixer *)mixer;
-	return om->SetVolume(volume, error);
-}
-
 const MixerPlugin oss_mixer_plugin = {
 	oss_mixer_init,
-	oss_mixer_finish,
-	oss_mixer_open,
-	oss_mixer_close,
-	oss_mixer_get_volume,
-	oss_mixer_set_volume,
 	true,
 };
diff --git a/src/mixer/plugins/PulseMixerPlugin.cxx b/src/mixer/plugins/PulseMixerPlugin.cxx
index 7c6076bb2..10aa6a93a 100644
--- a/src/mixer/plugins/PulseMixerPlugin.cxx
+++ b/src/mixer/plugins/PulseMixerPlugin.cxx
@@ -34,74 +34,95 @@
 
 #include <assert.h>
 
-struct PulseMixer final : public Mixer {
+class PulseMixer final : public Mixer {
 	PulseOutput *output;
 
 	bool online;
 	struct pa_cvolume volume;
 
+public:
 	PulseMixer(PulseOutput *_output)
 		:Mixer(pulse_mixer_plugin),
 		output(_output), online(false)
 	{
 	}
+
+	virtual ~PulseMixer();
+
+	void Offline();
+	void VolumeCallback(const pa_sink_input_info *i, int eol);
+	void Update(pa_context *context, pa_stream *stream);
+
+	/* virtual methods from class Mixer */
+	virtual bool Open(gcc_unused Error &error) override {
+		return true;
+	}
+
+	virtual void Close() override {
+	}
+
+	virtual int GetVolume(Error &error) override;
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static constexpr Domain pulse_mixer_domain("pulse_mixer");
 
-static void
-pulse_mixer_offline(PulseMixer *pm)
+void
+PulseMixer::Offline()
 {
-	if (!pm->online)
+	if (!online)
 		return;
 
-	pm->online = false;
+	online = false;
 
 	GlobalEvents::Emit(GlobalEvents::MIXER);
 }
 
-/**
- * Callback invoked by pulse_mixer_update().  Receives the new mixer
- * value.
- */
-static void
-pulse_mixer_volume_cb(gcc_unused pa_context *context, const pa_sink_input_info *i,
-		      int eol, void *userdata)
+inline void
+PulseMixer::VolumeCallback(const pa_sink_input_info *i, int eol)
 {
-	PulseMixer *pm = (PulseMixer *)userdata;
-
 	if (eol)
 		return;
 
 	if (i == nullptr) {
-		pulse_mixer_offline(pm);
+		Offline();
 		return;
 	}
 
-	pm->online = true;
-	pm->volume = i->volume;
+	online = true;
+	volume = i->volume;
 
 	GlobalEvents::Emit(GlobalEvents::MIXER);
 }
 
+/**
+ * Callback invoked by pulse_mixer_update().  Receives the new mixer
+ * value.
+ */
 static void
-pulse_mixer_update(PulseMixer *pm,
-		   struct pa_context *context, struct pa_stream *stream)
+pulse_mixer_volume_cb(gcc_unused pa_context *context, const pa_sink_input_info *i,
+		      int eol, void *userdata)
 {
-	pa_operation *o;
+	PulseMixer *pm = (PulseMixer *)userdata;
+	pm->VolumeCallback(i, eol);
+}
 
+inline void
+PulseMixer::Update(pa_context *context, pa_stream *stream)
+{
 	assert(context != nullptr);
 	assert(stream != nullptr);
 	assert(pa_stream_get_state(stream) == PA_STREAM_READY);
 
-	o = pa_context_get_sink_input_info(context,
-					   pa_stream_get_index(stream),
-					   pulse_mixer_volume_cb, pm);
+	pa_operation *o =
+		pa_context_get_sink_input_info(context,
+					       pa_stream_get_index(stream),
+					       pulse_mixer_volume_cb, this);
 	if (o == nullptr) {
 		FormatError(pulse_mixer_domain,
 			    "pa_context_get_sink_input_info() failed: %s",
 			    pa_strerror(pa_context_errno(context)));
-		pulse_mixer_offline(pm);
+		Offline();
 		return;
 	}
 
@@ -132,14 +153,14 @@ pulse_mixer_on_connect(gcc_unused PulseMixer *pm,
 void
 pulse_mixer_on_disconnect(PulseMixer *pm)
 {
-	pulse_mixer_offline(pm);
+	pm->Offline();
 }
 
 void
 pulse_mixer_on_change(PulseMixer *pm,
 		      struct pa_context *context, struct pa_stream *stream)
 {
-	pulse_mixer_update(pm, context, stream);
+	pm->Update(context, stream);
 }
 
 static Mixer *
@@ -162,65 +183,48 @@ pulse_mixer_init(gcc_unused EventLoop &event_loop, void *ao,
 	return pm;
 }
 
-static void
-pulse_mixer_finish(Mixer *data)
+PulseMixer::~PulseMixer()
 {
-	PulseMixer *pm = (PulseMixer *) data;
-
-	pulse_output_clear_mixer(pm->output, pm);
-
-	delete pm;
+	pulse_output_clear_mixer(output, this);
 }
 
-static int
-pulse_mixer_get_volume(Mixer *mixer, gcc_unused Error &error)
+int
+PulseMixer::GetVolume(gcc_unused Error &error)
 {
-	PulseMixer *pm = (PulseMixer *) mixer;
-	int ret;
-
-	pulse_output_lock(pm->output);
+	pulse_output_lock(output);
 
-	ret = pm->online
-		? (int)((100*(pa_cvolume_avg(&pm->volume)+1))/PA_VOLUME_NORM)
+	int result = online
+		? (int)((100 * (pa_cvolume_avg(&volume) + 1)) / PA_VOLUME_NORM)
 		: -1;
 
-	pulse_output_unlock(pm->output);
+	pulse_output_unlock(output);
 
-	return ret;
+	return result;
 }
 
-static bool
-pulse_mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
+bool
+PulseMixer::SetVolume(unsigned new_volume, Error &error)
 {
-	PulseMixer *pm = (PulseMixer *) mixer;
-	struct pa_cvolume cvolume;
-	bool success;
-
-	pulse_output_lock(pm->output);
+	pulse_output_lock(output);
 
-	if (!pm->online) {
-		pulse_output_unlock(pm->output);
+	if (!online) {
+		pulse_output_unlock(output);
 		error.Set(pulse_mixer_domain, "disconnected");
 		return false;
 	}
 
-	pa_cvolume_set(&cvolume, pm->volume.channels,
-		       (pa_volume_t)volume * PA_VOLUME_NORM / 100 + 0.5);
-	success = pulse_output_set_volume(pm->output, &cvolume, error);
+	struct pa_cvolume cvolume;
+	pa_cvolume_set(&cvolume, volume.channels,
+		       (pa_volume_t)new_volume * PA_VOLUME_NORM / 100 + 0.5);
+	bool success = pulse_output_set_volume(output, &cvolume, error);
 	if (success)
-		pm->volume = cvolume;
-
-	pulse_output_unlock(pm->output);
+		volume = cvolume;
 
+	pulse_output_unlock(output);
 	return success;
 }
 
 const MixerPlugin pulse_mixer_plugin = {
 	pulse_mixer_init,
-	pulse_mixer_finish,
-	nullptr,
-	nullptr,
-	pulse_mixer_get_volume,
-	pulse_mixer_set_volume,
 	false,
 };
diff --git a/src/mixer/plugins/PulseMixerPlugin.hxx b/src/mixer/plugins/PulseMixerPlugin.hxx
index 993945e9b..23cf03566 100644
--- a/src/mixer/plugins/PulseMixerPlugin.hxx
+++ b/src/mixer/plugins/PulseMixerPlugin.hxx
@@ -20,7 +20,7 @@
 #ifndef MPD_PULSE_MIXER_PLUGIN_HXX
 #define MPD_PULSE_MIXER_PLUGIN_HXX
 
-struct PulseMixer;
+class PulseMixer;
 struct pa_context;
 struct pa_stream;
 
diff --git a/src/mixer/plugins/RoarMixerPlugin.cxx b/src/mixer/plugins/RoarMixerPlugin.cxx
index f03c82c04..d1ac8a6e3 100644
--- a/src/mixer/plugins/RoarMixerPlugin.cxx
+++ b/src/mixer/plugins/RoarMixerPlugin.cxx
@@ -24,13 +24,25 @@
 #include "output/plugins/RoarOutputPlugin.hxx"
 #include "Compiler.h"
 
-struct RoarMixer final : public Mixer {
+class RoarMixer final : public Mixer {
 	/** the base mixer class */
 	RoarOutput *self;
 
+public:
 	RoarMixer(RoarOutput *_output)
 		:Mixer(roar_mixer_plugin),
 		self(_output) {}
+
+	/* virtual methods from class Mixer */
+	virtual bool Open(gcc_unused Error &error) override {
+		return true;
+	}
+
+	virtual void Close() override {
+	}
+
+	virtual int GetVolume(Error &error) override;
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static Mixer *
@@ -41,35 +53,19 @@ roar_mixer_init(gcc_unused EventLoop &event_loop, void *ao,
 	return new RoarMixer((RoarOutput *)ao);
 }
 
-static void
-roar_mixer_finish(Mixer *data)
-{
-	RoarMixer *self = (RoarMixer *) data;
-
-	delete self;
-}
-
-static int
-roar_mixer_get_volume(Mixer *mixer, gcc_unused Error &error)
+int
+RoarMixer::GetVolume(gcc_unused Error &error)
 {
-	RoarMixer *self = (RoarMixer *)mixer;
-	return roar_output_get_volume(self->self);
+	return roar_output_get_volume(self);
 }
 
-static bool
-roar_mixer_set_volume(Mixer *mixer, unsigned volume,
-		      gcc_unused Error &error)
+bool
+RoarMixer::SetVolume(unsigned volume, gcc_unused Error &error)
 {
-	RoarMixer *self = (RoarMixer *)mixer;
-	return roar_output_set_volume(self->self, volume);
+	return roar_output_set_volume(self, volume);
 }
 
 const MixerPlugin roar_mixer_plugin = {
 	roar_mixer_init,
-	roar_mixer_finish,
-	nullptr,
-	nullptr,
-	roar_mixer_get_volume,
-	roar_mixer_set_volume,
 	false,
 };
diff --git a/src/mixer/plugins/SoftwareMixerPlugin.cxx b/src/mixer/plugins/SoftwareMixerPlugin.cxx
index ec7aa197b..7dba2ee5e 100644
--- a/src/mixer/plugins/SoftwareMixerPlugin.cxx
+++ b/src/mixer/plugins/SoftwareMixerPlugin.cxx
@@ -38,7 +38,7 @@ CreateVolumeFilter()
 			  IgnoreError());
 }
 
-struct SoftwareMixer final : public Mixer {
+class SoftwareMixer final : public Mixer {
 	Filter *filter;
 
 	/**
@@ -51,6 +51,7 @@ struct SoftwareMixer final : public Mixer {
 
 	unsigned volume;
 
+public:
 	SoftwareMixer()
 		:Mixer(software_mixer_plugin),
 		 filter(CreateVolumeFilter()),
@@ -60,10 +61,26 @@ struct SoftwareMixer final : public Mixer {
 		assert(filter != nullptr);
 	}
 
-	~SoftwareMixer() {
+	virtual ~SoftwareMixer() {
 		if (owns_filter)
 			delete filter;
 	}
+
+	Filter *GetFilter();
+
+	/* virtual methods from class Mixer */
+	virtual bool Open(gcc_unused Error &error) override {
+		return true;
+	}
+
+	virtual void Close() override {
+	}
+
+	virtual int GetVolume(gcc_unused Error &error) override {
+		return volume;
+	}
+
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static Mixer *
@@ -74,59 +91,40 @@ software_mixer_init(gcc_unused EventLoop &event_loop, gcc_unused void *ao,
 	return new SoftwareMixer();
 }
 
-static void
-software_mixer_finish(Mixer *data)
+bool
+SoftwareMixer::SetVolume(unsigned new_volume, gcc_unused Error &error)
 {
-	SoftwareMixer *sm = (SoftwareMixer *)data;
-
-	delete sm;
-}
+	assert(new_volume <= 100);
 
-static int
-software_mixer_get_volume(Mixer *mixer, gcc_unused Error &error)
-{
-	SoftwareMixer *sm = (SoftwareMixer *)mixer;
+	if (new_volume >= 100)
+		new_volume = PCM_VOLUME_1;
+	else if (new_volume > 0)
+		new_volume = pcm_float_to_volume((exp(new_volume / 25.0) - 1) /
+						 (54.5981500331F - 1));
 
-	return sm->volume;
-}
-
-static bool
-software_mixer_set_volume(Mixer *mixer, unsigned volume,
-			  gcc_unused Error &error)
-{
-	SoftwareMixer *sm = (SoftwareMixer *)mixer;
-
-	assert(volume <= 100);
-
-	sm->volume = volume;
-
-	if (volume >= 100)
-		volume = PCM_VOLUME_1;
-	else if (volume > 0)
-		volume = pcm_float_to_volume((exp(volume / 25.0) - 1) /
-					     (54.5981500331F - 1));
-
-	volume_filter_set(sm->filter, volume);
+	volume = new_volume;
+	volume_filter_set(filter, new_volume);
 	return true;
 }
 
 const MixerPlugin software_mixer_plugin = {
 	software_mixer_init,
-	software_mixer_finish,
-	nullptr,
-	nullptr,
-	software_mixer_get_volume,
-	software_mixer_set_volume,
 	true,
 };
 
+inline Filter *
+SoftwareMixer::GetFilter()
+{
+	assert(owns_filter);
+
+	owns_filter = false;
+	return filter;
+}
+
 Filter *
 software_mixer_get_filter(Mixer *mixer)
 {
 	SoftwareMixer *sm = (SoftwareMixer *)mixer;
 	assert(sm->IsPlugin(software_mixer_plugin));
-	assert(sm->owns_filter);
-
-	sm->owns_filter = false;
-	return sm->filter;
+	return sm->GetFilter();
 }
diff --git a/src/mixer/plugins/WinmmMixerPlugin.cxx b/src/mixer/plugins/WinmmMixerPlugin.cxx
index 5e5a84637..d69480264 100644
--- a/src/mixer/plugins/WinmmMixerPlugin.cxx
+++ b/src/mixer/plugins/WinmmMixerPlugin.cxx
@@ -30,13 +30,25 @@
 #include <math.h>
 #include <windows.h>
 
-struct WinmmMixer final : public Mixer {
+class WinmmMixer final : public Mixer {
 	WinmmOutput *output;
 
+public:
 	WinmmMixer(WinmmOutput *_output)
 		:Mixer(winmm_mixer_plugin),
 		output(_output) {
 	}
+
+	/* virtual methods from class Mixer */
+	virtual bool Open(gcc_unused Error &error) override {
+		return true;
+	}
+
+	virtual void Close() override {
+	}
+
+	virtual int GetVolume(Error &error) override;
+	virtual bool SetVolume(unsigned volume, Error &error) override;
 };
 
 static constexpr Domain winmm_mixer_domain("winmm_mixer");
@@ -64,20 +76,11 @@ winmm_mixer_init(gcc_unused EventLoop &event_loop, void *ao,
 	return new WinmmMixer((WinmmOutput *)ao);
 }
 
-static void
-winmm_mixer_finish(Mixer *data)
-{
-	WinmmMixer *wm = (WinmmMixer *)data;
-
-	delete wm;
-}
-
-static int
-winmm_mixer_get_volume(Mixer *mixer, Error &error)
+int
+WinmmMixer::GetVolume(Error &error)
 {
-	WinmmMixer *wm = (WinmmMixer *) mixer;
 	DWORD volume;
-	HWAVEOUT handle = winmm_output_get_handle(wm->output);
+	HWAVEOUT handle = winmm_output_get_handle(output);
 	MMRESULT result = waveOutGetVolume(handle, &volume);
 
 	if (result != MMSYSERR_NOERROR) {
@@ -88,12 +91,11 @@ winmm_mixer_get_volume(Mixer *mixer, Error &error)
 	return winmm_volume_decode(volume);
 }
 
-static bool
-winmm_mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
+bool
+WinmmMixer::SetVolume(unsigned volume, Error &error)
 {
-	WinmmMixer *wm = (WinmmMixer *) mixer;
 	DWORD value = winmm_volume_encode(volume);
-	HWAVEOUT handle = winmm_output_get_handle(wm->output);
+	HWAVEOUT handle = winmm_output_get_handle(output);
 	MMRESULT result = waveOutSetVolume(handle, value);
 
 	if (result != MMSYSERR_NOERROR) {
@@ -106,10 +108,5 @@ winmm_mixer_set_volume(Mixer *mixer, unsigned volume, Error &error)
 
 const MixerPlugin winmm_mixer_plugin = {
 	winmm_mixer_init,
-	winmm_mixer_finish,
-	nullptr,
-	nullptr,
-	winmm_mixer_get_volume,
-	winmm_mixer_set_volume,
 	false,
 };