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//! How to parse "key=value" pairs with structopt.
use std::error::Error;
use structopt::StructOpt;
/// Parse a single key-value pair
fn parse_key_val<T, U>(s: &str) -> Result<(T, U), Box<dyn Error>>
where
T: std::str::FromStr,
T::Err: Error + 'static,
U: std::str::FromStr,
U::Err: Error + 'static,
{
let pos = s
.find('=')
.ok_or_else(|| format!("invalid KEY=value: no `=` found in `{}`", s))?;
Ok((s[..pos].parse()?, s[pos + 1..].parse()?))
}
#[derive(StructOpt, Debug)]
struct Opt {
// number_of_values = 1 forces the user to repeat the -D option for each key-value pair:
// my_program -D a=1 -D b=2
// Without number_of_values = 1 you can do:
// my_program -D a=1 b=2
// but this makes adding an argument after the values impossible:
// my_program -D a=1 -D b=2 my_input_file
// becomes invalid.
#[structopt(short = "D", parse(try_from_str = parse_key_val), number_of_values = 1)]
defines: Vec<(String, i32)>,
}
fn main() {
let opt = Opt::from_args();
println!("{:?}", opt);
}
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