Imagine we're building a utility for joining MP3 files, something like MP3cat. We want the user to supply the file names as a list of command line arguments. We also want to support an --out/-o option so the user can specify an output filename and a --quiet/-q flag for turning down the program's verbosity.

let parser = ArgParser()
    .helptext("Usage: mp3cat...")
    .version("1.0")
    .option("out o")
    .flag("quiet q")

That's it, we're done specifying our interface. Now we can parse the program's arguments:

parser.parse()

This will exit with a suitable error message for the user if anything goes wrong. Now we can check if the --quiet flag was found:

if parser.found("quiet") {
    doStuff()
}

And determine our output filepath:

let filepath = parser.value("out") ?? "output.mp3"

The input filenames will be collected by the parser into an array of positional arguments:

for filename in parser.args {
    doStuff()
}