Attribute Macro optfn

#[optfn]

Optional arguments for functions! Add optfn on top of any function and then you can call the funtion with optional arguments.

Note that this still obeys traditional macro_rules, so you can only use the macro after declaration or import it from “crate”.

#[optargs::optfn]
pub fn plot(
    x: Vec<i32>,
    y: Option<Vec<i32>>,
    title: Option<&str>,
    xlabel: Option<&str>,
    ylabel: Option<&str>,
    legend: Option<bool>
) {}

// can now call it with optional arguments
plot!(
    x: vec![1,2,3],
    y: vec![1,2,3],
    title: "Awesome plot",
    xlabel: "x axis",
    ylabel: "y axis"
);