tagged_err_union.zig

const E = error(union) {
  StringError: []const u8,
  IntError: i32,
  VoidError,
};

fn example(input: isize) !void {
    if (input < 0) {
        return error { .StringError = "input less than 0" };
    }
    // do something useful
    var value = // some boolean value
    if (value) {
        return error.VoidError;
    }
}

fn usage() void {
    example(-1) catch |err| {
        switch (err) {
            error.StringError => |string| // do something useful,
            error.IntError => |int| // do something useful,
            error.VoidError => // do something useful,
        }
    };
}