Arg.java

public interface CommandArg<T> {
    Text getName();
    TypeToken<T> getType();
}

public interface CommandArgs {
    <T> T getOne(CommandArg<T> arg) throws NoSuchElementException;
    <T> Optional<T> getOne(Text arg);
}

CommandArg<Text> name = text(Text.of("name"));
CommandArg<Optional<Text>> desc = optional(text(Text.of("desc")));

public void onCmd(CommandSource src, CommandArgs args) {
    Text name = args.getOne(this.name);
    Optional<Text> desc = args.getOne(this.desc);
}