Template class for Rust-like error handling, based on the suggestion from https://softwareengineering.stackexchange.com/questions/352702/error-handling-considerations/352745

Basically, instead of exceptions, you can implement functions that return Variant class that contains either return value or error details, if function call has failed for some reason.

Moreover, you can use TRY macro to chain multiple calls like this:

// If establishConnection() fails, getTemperature() will not be called.
double temperature = TRY( TRY(establishConnection())->getTemperature() );

There are four main differences:

1. Trying to call getData (or typecast) the Result object with isOk() == falsewill throw std::logic_error exception.
2. I had to drop C++11 and C++17 features to provide C99 support. (technically it is possible to detect which standard is being used from preprocessor directives and use the correct set of features but I was lazy)
3. If GNU statement expressions are not supported by your compiler, it is possible to use TRY_2 macro that doesn't depend on those. It was implemented based on the ideas from this article: https://www.artima.com/articles/conditional-love-foreach-redux
4. Instead of [[nodiscard]] from C++17, I'm using GCC-specific warn_unused_result to show compiler warnings for ignored errors.

List of removed features from newer C++ standards:

• Add std::move statements for C++11 version
• Use 'auto' for C++11 version
• Use [[nodiscard]] for Result in C++17 version

Note that it might be possible to use union for data and err_val class members to reduce memory usage. I'm not sure if it is always possible.