Has anyone ever had a use for the __COUNTER__ pre-processor macro?

Question

The __COUNTER__ symbol is provided by VC++ and GCC, and gives an increasing non-negative integral value each time it is used.

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Answer 1

A usage is in TensorFlow's REGISTER_KERNEL_BUILDER macro. Each TensorFlow Op could have one or more kernels as its implementations. These kernels are registered with a registrar. The registration of a kernel is done by defining a global variable -- the constructor of the variable can do the registration. Here the authors use __COUNTER__ to give each global variable a unique name.

#define REGISTER_KERNEL_BUILDER(kernel_builder, ...) \
  REGISTER_KERNEL_BUILDER_UNIQ_HELPER(__COUNTER__, kernel_builder, __VA_ARGS__)

#define REGISTER_KERNEL_BUILDER_UNIQ_HELPER(ctr, kernel_builder, ...) \
  REGISTER_KERNEL_BUILDER_UNIQ(ctr, kernel_builder, __VA_ARGS__)

#define REGISTER_KERNEL_BUILDER_UNIQ(ctr, kernel_builder, ...)          \
  static ::tensorflow::kernel_factory::OpKernelRegistrar                \
  registrar__body__##ctr##__object(                                 \
      SHOULD_REGISTER_OP_KERNEL(#__VA_ARGS__)                       \
      ? ::tensorflow::register_kernel::kernel_builder.Build()   \
      : nullptr,                                                \
      #__VA_ARGS__, [](::tensorflow::OpKernelConstruction* context) \
            -> ::tensorflow::OpKernel* {                \
              return new __VA_ARGS__(context);          \
            });