dynarg

A simple dynamic argument system

Have you ever wanted to have multiple functions with the same signature, but with very different purposes and behavior?

• Maybe you want to make an image editing app, with lots of tools.
• Maybe you want to make a Rust GCODE implementation.
• Maybe you just want to make a modular shell program and dynamically pick arguments out like fruits off a berry bush, while keeping track of which ones haven't been used.

Regardless, you probably want an API that can:

• Match arguments to static strings, to avoid runtime overhead, while maintaining readability.
• Potentially handle dynamic strings if needed.
• Handle arbitrary argument types.
• Provide convenience functions for working with arguments -- e.g., wrapper functions for common types.

If any of this applies to you, this is a library to consider. Note that for very high-performance applications, it might be better to roll your own custom use case with a Vec (ideally recycled!) of enum, to avoid dynamic dispatch.

This API is at this point considered stable and reasonably mature. It is forbid_unsafe, and written in pure Rust.

Basic example

use dynarg::Args;

fn main() {
    // Creating Args object
    let mut args = Args::new();
    // Inserting a string type
    args.insert_string("greeting", String::from("hello world"));
    // Inserting an i32 type
    args.insert_i32("meaning_of_life", 42);
    // There's a lot more types where that came from, BTW :)
    // (In fact, you can use any type that implements `Any`,
    // which... I think should be any?)
    
    // Retrieving string type
    let out = args.get_string("greeting").unwrap();
    println!("{}", out);
    // Retrieving i32
    let meaning_of_life = args.get_i32("meaning_of_life").unwrap();
    println!("The meaning of life is: {}", meaning_of_life);
}

Tracking which argument is used

use dynarg::Args;

fn main() {
    // Creating Args object
    let mut args = Args::new();
    // Inserting a string type
    args.insert_string("greeting", String::from("hello world"));
    // Inserting an i32 type
    args.insert_i32("meaning_of_life", 42);
    // There's a lot more types where that came from, BTW :)
    // (In fact, you can use any type that implements `Any`, which... I think should be any?)
        
    // Retrieving string type (while marking used flag!)
    let out = args.poke_string("greeting").unwrap();
    println!("{}", out);
    // Retrieving i32 (also while marking used flag!)
    let meaning_of_life = args.poke_i32("meaning_of_life").unwrap();
    println!("The meaning of life is: {}", meaning_of_life);
    // NOTE: the difference between poke and poke_* functions, and get and get_,
    // is that poke marks the status as used.
    // Note that this only exists if `used` feature is enabled for library.
    // Explicitly marking status is used is useful for sanity checking -- e.g.
    
    // Checking used status of args is useful for catching
    // what would otherwise be silent or hard-to-catch errors
    if args.all_used() {
        println!("All used! :3");
    } else {
        for used_arg_name in args.iter_not_used_name() {
            println!("Arg: \"{}\" not used", used_arg_name);
        }
    }
}

Less basic example

use dynarg::*;

/// Where normally you'd need to have a fixed set of arguments,
/// each of which would be roughly fixed types
/// -- you can dynamically push arguments on the fly instead.
/// This is useful when you need a consistent function signature
/// for different types of functions,
/// each needing different arguments
fn draw(args: &mut Args) {
    if let Ok(greeting) = args.poke_string("greeting") {
        println!("{} world", greeting);
    }
    if let Ok(arg) = args.poke::<Fruit>("fruit_to_draw") {
        println!("I will draw {}!", arg.0);
        if let Ok(size) = args.poke::<f32>("size") {
            println!("with a size of {}", size);
        }
    } else {
        panic!("Nothing to draw D:");
    }
}

/// A custom struct as an example
struct Fruit<'a>(&'a str);

fn main() {
   let mut args = Args::default();

    let apple = Fruit("apple");
    // This is how you add arguments
    args.insert("fruit_to_draw", Box::new(apple));
    args.insert("size", Box::new(5.2f32));
    let greeting = String::from("henlo");
    args.insert_string("greeting", greeting);
    draw(&mut args);
    if !args.all_used() {
        println!("Warning! I didn't use all my arguments D:");
    }
    // Clear all the used flags on args
    args.reset_used_status();
}

Github available here.

PRs welcome :)

Todo

• Custom type handling
• Replace Options with Results such that it's possible to identify whether the argument name didn't exist, or the type was wrong
• Add snafu
• Add convenience functions (e.g. get_string(), get_int())
• Properly document gotchas
• Add variant without used() functionality.
• Add more examples
• Benchmarks