making default functions to closures

[thinkrapido]

I like to suggest a pull request to make the default functions like ModelFn, UpdateFn, etc... usable as a closure.

Related: #793

It is a very easy fix and we gain much more flexibility in developing complex programs.

A call would be via an macro

fn main() {
    nannou::sketch(view!(|app: &App, frame: Frame| {
        //...
    })).run()
}

and to respective functions.

Also read, how it is meant: https://medium.com/@romeo-disca/smart-pointers-in-rust-158046006f15

[thinkrapido]

all the examples need to be improved due to this pull request

[Woyten]

Using closures instead of fns would make things easier, indeed. In my personal project, for example, I am using thread_local! to pass a pre-computed value to the fn. However, there are certain things in your PR I do not understand:

• Why are the types Arc<dyn Fn(...)>? Shared Fn closures are a pretty rare thing in Rust. You probably want to use Box<dyn FnMut(...)>.
• What is the reason to use macros? You could just use regular generics instead e.g. fn foo(foo_fn: impl FnMut()) { let boxed = Box::new(foo_fn) }. If you want some kind of name aliasing you could do the following:

trait FooFn {
    fn foo(&mut self);
}

impl<F: FnMut()> FooFn for F {
    fn foo(&mut self) {
        self()
    }
}

fn consumes_foo(foo_fn: impl FooFn) {
    let boxed: Box<dyn FooFn> = Box::new(foo_fn);
}

fn calls_foo() {
    consumes_foo(|| {})
}

[abey79]

@thinkrapido Did you make any progresses with this PR? I just ran into the issue of passing state from outside nannou::app(), which it would solve.

[thinkrapido]

@abey79 , no I didn't. For me the pull request solved to problem.