Macro clap_dispatch 

macro_rules! clap_dispatch {
    ($matches:expr; { $( $name:ident $match_arm_args:tt => $callback:expr ),* }) => { ... };
    (MATCH_ARM_ARGS, $matches:ident, ( $matches_name:pat, $($arg_name:ident as $varname:ident),* )) => { ... };
    (MATCH_ARM_ARGS, $matches:ident, ( $matches_name:pat )) => { ... };
    (MATCH_ARM_ARGS, $matches:ident, ()) => { ... };
}

Process a clap::ArgMatches with pattern-matching-like syntax.

use self::clap::*;
   let matches = App::new("test")
       .subcommand(SubCommand::with_name("sub")
           .subcommand(SubCommand::with_name("subsub")
               .arg(Arg::with_name("TEST_ARG").index(1))))
       .subcommand(SubCommand::with_name("othersub"))
       .get_matches_from(vec!["test", "sub", "subsub", "fooarg"]);

   let mut called = false;
   clap_dispatch!(matches; {
       sub(sub_matches) => clap_dispatch!(sub_matches; {
           subsub(_, TEST_ARG as test_arg) => {
               assert_eq!(test_arg, "fooarg");
               called = true;
           }
       }),
       othersub() => { panic!("Should not have been called."); }
   });

   assert!(called);