Clap 3 Beta: Add default values using @args macro

[HerbM]

[Rust & clap newbie using clap 3.x beta to parse args]

Problem and goal is to add defaults to @arg within the myapp .

I am using

clap_app!(myapp =>
    (@arg PORT: -p --port ... +takes_value "Port to test")  // <<< Add a default value here, e.g., 135 or 22, or [135 22]
    // more arg macros lines
)  

It may be the case that I've chosen badly by using the @arg macro instead of one of the other (more flexible?) clap choices.
FYI: I get the multiple PORT values (in an vec) and can iterate over them but want to add a default within the clap setup (rather than later in the calling code).

As a side note, is there a method to use any of the other styles with the macro style for clap or do I just rewrite it to use features not (easily) supported by the macro style?

Also, it would be nice to make the default OS specific, "Unixy" vs. Windows.
The idea would be to default to 22 on Linux and 135 on Windows since those are typically open (if not blocked by firewalls etc.)

The docs don't seem to have an example for any clap shortcuts for doing either of these, but they do suggest both are possible.

Thanks for any help. I read a lot of the docs, searched the examples directory, and Google a bunch of articles. Probably because 3.x is in Beta.

[CreepySkeleton]

Yes, the documentation for the macro is terrible. We would very much appreciate any help there!

You can call any method from Arg via method(arg) syntax.

clap_app!(myapp =>
    (@arg PORT: -p --port ... +takes_value default_value("22") "Port to test") 
)  

Playground

And you don't need any special support from clap for OS-specific config:

#[cfg(windows)]
const PORT: &str = "135";
#[cfg(not(windows))]
const PORT: &str = "22";

clap_app!(myapp =>
    (@arg PORT: -p --port ... +takes_value default_value(PORT) "Port to test") 
)  

[HerbM]

@CreepySkeleton
Thank you and I would not have labeled the macro docs "terrible" -- just not as fully developed as some of the other methods with full examples, and this is a Beta.
It's nice work.
Thanks so much for direct help and so quickly.

So seeing I can call "any method" from @arg seems to answer quite a few questions I've haven't even thought of yet.