output/Interface: convert to abstract class

Yet another C-style vtable replaced with C++.

src/output/plugins/PipeOutputPlugin.cxx

@@ -20,7 +20,6 @@
 #include "config.h"
 #include "PipeOutputPlugin.hxx"
 #include "../OutputAPI.hxx"
-#include "../Wrapper.hxx"
 #include "system/Error.hxx"
 
 #include <string>
@@ -28,43 +27,36 @@
 
 #include <stdio.h>
 
-class PipeOutput {
-	friend struct AudioOutputWrapper<PipeOutput>;
-
-	AudioOutput base;
-
+class PipeOutput final : AudioOutput {
 	const std::string cmd;
 	FILE *fh;
 
 	PipeOutput(const ConfigBlock &block);
 
 public:
-	static PipeOutput *Create(EventLoop &event_loop,
-				  const ConfigBlock &block);
+	static AudioOutput *Create(EventLoop &,
+				   const ConfigBlock &block) {
+		return new PipeOutput(block);
+	}
 
-	void Open(AudioFormat &audio_format);
+private:
+	void Open(AudioFormat &audio_format) override;
 
-	void Close() {
+	void Close() noexcept override {
 		pclose(fh);
 	}
 
-	size_t Play(const void *chunk, size_t size);
+	size_t Play(const void *chunk, size_t size) override;
 };
 
 PipeOutput::PipeOutput(const ConfigBlock &block)
-	:base(pipe_output_plugin),
+	:AudioOutput(0),
 	 cmd(block.GetBlockValue("command", ""))
 {
 	if (cmd.empty())
 		throw std::runtime_error("No \"command\" parameter specified");
 }
 
-inline PipeOutput *
-PipeOutput::Create(EventLoop &, const ConfigBlock &block)
-{
-	return new PipeOutput(block);
-}
-
 inline void
 PipeOutput::Open(gcc_unused AudioFormat &audio_format)
 {
@@ -83,22 +75,9 @@ PipeOutput::Play(const void *chunk, size_t size)
 	return nbytes;
 }
 
-typedef AudioOutputWrapper<PipeOutput> Wrapper;
-
 const struct AudioOutputPlugin pipe_output_plugin = {
 	"pipe",
 	nullptr,
-	&Wrapper::Init,
-	&Wrapper::Finish,
-	nullptr,
-	nullptr,
-	&Wrapper::Open,
-	&Wrapper::Close,
-	nullptr,
-	nullptr,
-	&Wrapper::Play,
-	nullptr,
-	nullptr,
-	nullptr,
+	&PipeOutput::Create,
 	nullptr,
 };