How to create a new Struct out of multiple values for an argument?

[mnpw]

Is there a way to combine an Arg with multiple values into an Struct? I want to take 2 values for replicaof and combine them into Replica type.

#[derive(Args, Debug, Clone)]
struct Replica {
    host: String,
    port: u16,
}

impl From<Vec<String>> for Replica {
    todo!();
}

#[derive(Parser, Debug)]
struct Config {
    #[arg(long, default_value = "127.0.0.1")]
    host: String,
    #[arg(long, default_value_t = 6379)]
    port: u16,
    #[arg(long, num_args = 2, value_name = "REPLICA_HOST REPLICA_PORT")]
    replicaof: Option<Replica>, // This doesn't work
    // replicaof: Option<Vec<String>> -> This works
}

fn main() {
    let config = Config::parse_from(["cmd", "--host", "www.example.com", "--port", "1234", "--replicaof", "localhost", "6666"])
    assert_eq!(config, Config { 
        host: "www.example.com".to_owned(),
        port: 1234,
        replicaof: Replica {
            host: "localhost".to_owned(),
            port: 6666,
        },
    );
}

I tried using a custom parser but the input to it only captures one value - localhost and not 6666.

#[derive(Parser, Debug)]
struct Config {
    ...
    #[arg(long, num_args = 2, value_parser = custom_parser, value_name = "REPLICA_HOST REPLICA_PORT")]
    replicaof: Option<Replica>,
}

fn custom_parser(input: &str) -> Result<Replica, String> {
    // input is "localhost", I expect it to be "localhost 6666"
}

[epage]

We only support using the same value parser across all values at this time. The subset of this for tuples is being tracked in #1717.

This can also be handled through delimiters within the value. In the specific example you gave, you could parse a single value as a URL which can have both a host and a port.