AdsrEnvelope has multiple definitions when compiling C++ patch with .cpp file provided

[TarkanAl-Kazily]

The way the AdsrEnvelope.h header is written, the specialized implementations for Linear and Exponential envelope types get defined multiple times when building a patch that uses a .cpp file, resulting in the Patch elf failing the linker step.

This is rather simple to reproduce just with two files implementing an empty Patch that just creates an AdsrEnvelope:

EnvelopeBugPatch.hpp

#ifndef __EnvelopeBugPatch_hpp__
#define __EnvelopeBugPatch_hpp__

#include "Patch.h"
#include "AdsrEnvelope.h"

class EnvelopeBugPatch : public Patch {
public:
  EnvelopeBugPatch() {
    env = LinearAdsrEnvelope::create(getSampleRate());
  }

  ~EnvelopeBugPatch() {
    LinearAdsrEnvelope::destroy(env);
  }

  void processAudio(AudioBuffer &buffer) override;

private:
  LinearAdsrEnvelope *env;
};

#endif // __EnvelopeBugPatch_hpp__

EnvelopeBugPatch.cpp

#include "EnvelopeBugPatch.hpp"

void EnvelopeBugPatch::processAudio(AudioBuffer &buffer) {}

The result when compiling these is a linker error:

$ make PATCHNAME=EnvelopeBug clean patch
Building patch EnvelopeBug
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<true>::increment(float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<true>::decrement(float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<false>::increment(float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<false>::decrement(float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<true>::calculateIncrement(float, float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<false>::calculateIncrement(float, float, float)'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<false>::MINLEVEL'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: ./Build/PatchProgram.o (symbol from plugin): in function `onMidiCallback(unsigned char, unsigned char, unsigned char, unsigned char)':
(.text+0x0): multiple definition of `AdsrEnvelope<true>::MINLEVEL'; ./Build/EnvelopeBugPatch.o (symbol from plugin):(.text+0x0): first defined here
/usr/lib/gcc/arm-none-eabi/12.2.0/../../../../arm-none-eabi/bin/ld: warning: Build/patch.elf has a LOAD segment with RWX permissions
collect2: error: ld returned 1 exit status
make[1]: *** [compile.mk:179: Build/patch.elf] Error 1
make: *** [Makefile:110: patch] Error 2

[antisvin]

There are 2 correct ways to use fully specialiazed templates - either in source file as described here, or keep them in the header file with inline keyword added. Moving them to a CPP file is probably preferable, as this would compile them just once when building static OWL library.

[TarkanAl-Kazily]

Here there are also two specialized templates used for a constant for which inline can't be used, so I took the approach to just create a new file.