Add support for negative boolean flags

[vmalloc]

Apologies if this is a duplicate or has already been requested -- but it would be nice to have a way to set a boolean flag which defaults to true unless it is given (e.g. --no-do-something would set the do_something field to false, otherwise it would be true)

[CreepySkeleton]

That would be clap's feature, you should open an issue there instead. Typically, if you have a feature request that adds some functionality to clap::App/Arg you should go there, not here. If it would require explicit support in structopt we'll be happy to do that but we need it implemented in clap::Arg in the first place.

By the way, there's such a request already, feel free to send a PR.

[TeXitoi]

As of today, you can also do the machinery by hand, I.e. creating a no-do-something flag on a do_something field, with a custom from_flag.

I'm on mobile, I'll try to write such an example within the day.

[vmalloc]

@CreepySkeleton I see. Thanks for the reply, and sorry for the spam!

[TeXitoi]

use structopt::StructOpt;

#[derive(Debug, StructOpt)]
struct Opt {
    #[structopt(long = "no-verbose", parse(from_flag = std::ops::Not::not))]
    verbose: bool,
}
fn main() {
    let cmd = Opt::from_args();
    println!("{:#?}", cmd); 
}

[vmalloc]

@TeXitoi awesome! Going to add it to my personal cookbook. That is exactly what I needed.

Thank you very much!

[TeXitoi]

Example proposed in #281

[ghost]

@TeXitoi
Hi, thank you for your great example.

I have an question, can I use switching flag...?

    #[structopt(long = "verbose")]
    #[structopt(long = "no-verbose", parse(from_flag = std::ops::Not::not))]
    pub verbose: bool,

// Of course this doesn't work, verbose gone away.

Looking at an issue #320 and #126, it looks not implemented yet.
But the issue is two years ago, so I wonder it actually implemented now.

[TeXitoi]

It's not. But you can do with 2 field, a verbose and a quiet, and implement a getter on your struct that read the 2 fields to decide what to return.

[ghost]

@TeXitoi
Thank you for answer.
I got it. Thank you very much!