Best practice to access arguments throughout an application

[mnlm]

Hi,

first time using clap, also new to Rust. Thanks for the crate, really enjoyed using it so far.
I'm wondering about the best way to access cli arguments in different functions.

Parse in fn main and pass everything through to the function that needs the argument:

/// main.rs
use clap::Parser;

#[derive(Parser)]
struct Cli {
    name: String,
    age: u8,
}

fn main() {
    let cli = Cli::parse();
    foo(cli.name, cli.age);
}

fn foo(name: String, age: u8) {
    println!("name: {}", name);
    bar(age);
}

fn bar(age: u8) {
    println!("age: {}", age);
}

Or is it better to parse again in the function where you need the actual argument:

/// main.rs
use clap::Parser;

#[derive(Parser)]
struct Cli {
    name: String,
    age: u8,
}

fn main() {
    let cli = Cli::parse();
    foo(cli.name);
}

fn foo(name: String) {
    println!("name: {}", name);
    bar();
}

fn bar() {
    let cli = Cli::parse();
    println!("age: {}", cli.age);
}

Or is there a different way entirely?

[epage]

The patterns I've seen used that seem to make the most sense

• Pass the individual fields around as needed
• Have an application wide Context that you put the fields into and pass that around
• When using subcommands, have run functions on the individual subcommands which directly read their structs

These can be mixed together. For example, cargo-release uses the subcommand run functions (https://github.com/crate-ci/cargo-release/blob/master/src/bin/cargo-release.rs) which will access individual fields (https://github.com/crate-ci/cargo-release/blob/master/src/steps/owner.rs#L42) but also layers parts of the struct into the config (https://github.com/crate-ci/cargo-release/blob/master/src/steps/owner.rs#L53) which kind of acts like a Context.

[mnlm]

• Have an application wide Context that you put the fields into and pass that around

Not exactly sure what you're referring to with Context. A struct you implement yourself called Context that holds all the arguments, or is it an actual Rust or crate data type (couldn't find anything appropriate here)?

[epage]

Context would be a struct you create that holds all of your applications "global" state.