Shared via Rust Playground

playground.rs

/*
struct Foo {
    data: Vec<u8>
}

impl Foo {
    fn p(&mut self, c: usize) {
        self.data.insert(0, (c + 42) as u8);
    }
    
    fn n<F>(&self, f: F) -> usize where 
    F: Fn(&[u8]) -> &[u8] {
        f(self.data.as_ref()).len()
    }
    
    fn a<F>(&self, f: F) -> &[u8] where
    F: Fn(&[u8]) -> &[u8]
    {
        f(self.data.as_ref())
    }
    
    fn fa<F>(&mut self, f: &F) -> &[u8] where
    F: Fn(&[u8]) -> &[u8]
    {
        let s = self.n(f);
        self.p(s);
        self.a(f)
    }
}
*/

/*
struct Foo<O> {
    data: Vec<O>
}

impl<O,> Foo<O> {
    fn d(&self) -> &[O] {
        self.data.as_ref()
    }
    
    fn p(&mut self, c: usize) {
        self.data.truncate(c);
    }
    
    fn n<'b, F, CO>(&'b self, f: F) -> usize where 
    F: Fn(&'b [O]) -> (&'b [O], CO) {
        f(self.d()).0.len()
    }
    
    fn a<'b, F, CO>(&'b self, f: F) -> CO where
    F: Fn(&'b [O]) -> (&'b [O], CO) {
        f(self.d()).1
    }
    
    fn fa<'b, F, CO>(&'b mut self, f: &F) -> CO where
    F: Fn(&'b [O]) -> (&'b [O], CO) {
        let s = self.n(f);
        self.p(s);
        self.a(f)
    }
}
*/

struct Foo<O> {
    data: Vec<O>
}

impl<O,> Foo<O> {
    fn d(&self) -> &[O] {
        self.data.as_ref()
    }
    
    fn p(&mut self, c: usize) {
        self.data.truncate(c);
    }
    
    fn n<'b, F, CO>(&'b self, f: F) -> usize where 
    F: Fn(&[O]) -> (&[O], CO) {
        f(self.d()).0.len()
    }
    
    fn a<'b, F, CO>(&'b self, f: F) -> CO where
    F: Fn(&[O]) -> (&[O], CO) {
        f(self.d()).1
    }
    
    fn fa<'b, F, CO>(&'b mut self, f: &F) -> CO where
    F: Fn(&[O]) -> (&[O], CO) {
        let s = self.n(f);
        self.p(s);
        self.a(f)
    }
}

fn x<F>(d: &[u8], f: F) -> &[u8] where
F: Fn(&[u8]) -> (&[u8], &[u8]) {
    f(d).1
}

fn main() {
    fn z(i: &[u8]) -> (&[u8], &[u8]) {
        (&i[0..5], &i[2..4])
    }
    fn y(i: &[u8]) -> (&[u8], u32) {
        (&i[0..5], 42)
    }
    
    let mut f = Foo { data: vec![0, 1, 2, 3, 4] };
    
    //println!("x: {:?}", x(&[1, 2, 3, 4, 5], z));
    //println!("x: {:?}", x(&[3, 4, 5, 6, 7], z));

    println!("bar: {:?}", f.fa(&z));
    println!("bar: {:?}", f.fa(&y));
}