rust-enum

This library is for those who miss using Rust enums in C++. It will give you the ability to create variants that can be matched. The only dependency is the Boost Preprocessor library.

Usage

To use rust-enum, you must first create your enum. You can do this with the $enum macro, like so:

$enum(name,
    (first),
    (second)(std::string, int),
    (third),
    (last)(std::vector<int>),
);

The first element in each declaration is the name, the second is the type (this will override the default enum type).

You can then use the $match macro to switch over the enum. The following is an example of this:

$match(instance,
    (first) ( 
        std::cout << "first" << std::endl; 
    ),
    (second)(foo, bar) (
        std::cout << "second: " << foo << ", " << bar << std::endl;
    ),
    (_) (
        std::cout << "default." << std::endl;
    )
)

The first element in each case is the variant you wish to switch over, and the second is the name of the created instance. Passing _ as the first argument without passing a name will set the default case.

$match also works with virtuals. The syntax is the same, and can be used out of the box (no custom definitions required).

Tips

While the $match macro is pretty, but isn't the most efficient. It has to generate paths for $enum and virtuals, even though only one is taken. To speed up preprocessing, you can use $fmatch for $enums, and $vmatch for virtuals. These will take a lot less time to process.

You can find a working example on Godbolt here.

Notes

If you run into any issues or have an idea, let me know!