Function understand_lifetime_early_late_bound

pub fn understand_lifetime_early_late_bound()

说明： 生命周期参数：late bound vs early bound

Quiz 11: https://dtolnay.github.io/rust-quiz/11

fn f<'a>() {}
fn g<'a: 'a>() {}

fn main() {
    let pf = f::<'static> as fn(); // late bound
    let pg = g::<'static> as fn(); // early bound
    print!("{}", pf == pg);
}

示例一：late bound lifetime

struct Buffer {
    buf: Vec<u8>,
    pos: usize,
}

impl Buffer {
    fn new() -> Buffer {
        Buffer {
            buf: vec![1,2,3, 4, 5,6],
            pos: 0,
        }
    }

    fn read_bytes<'a>(&'a mut self) -> &'a [u8] {
        self.pos += 3;
        &self.buf[self.pos-3..self.pos]
    }
}

fn print(b1 :&[u8], b2: &[u8]) {
    println!("{:#?} {:#?}", b1, b2)
}

fn main() {
    let mut buf = Buffer::new();
    // let b1 = buf.read_bytes(); // don't work
    let b1 = &(buf.read_bytes().to_owned());
    let b2 = buf.read_bytes();
    print(b1,b2)
}

示例二： early bound lifetime

fn main() {
    let v = vec![1,2,3, 4, 5,6];
    let mut buf = Buffer::new(&v);
    let b1 = buf.read_bytes();
    // let b1 = &buf.read_bytes().to_owned();
    let b2 = buf.read_bytes();
    print(b1,b2)
}

fn print(b1 :&[u8], b2: &[u8]) {
    println!("{:#?} {:#?}", b1, b2)
}

struct Buffer<'a> {
    buf: &'a [u8],
    pos: usize,
}

impl<'b, 'a: 'b> Buffer<'a> {
    fn new(b: &'a [u8]) -> Buffer {
        Buffer {
            buf: b,
            pos: 0,
        }
    }

    fn read_bytes(&'b mut self) -> &'a [u8] {
        self.pos += 3;
        &self.buf[self.pos-3..self.pos]
    }
}