如何返回對擁有和活着的東西的引用？

Question

如何在下面的代碼中正確地返回set函數中的引用？我確實知道變量set在塊結束時超出了範圍，但它所引用的數組是擁有且活着的。終身'b的嘗試是徒勞的。

#[derive(PartialEq, Eq, PartialOrd, Ord, Debug)] 
struct Appearance<'a> { 
    identity: &'a u64, 
    role:  &'a str 
} 

#[derive(Clone, Copy, Debug)] 
enum Dereference<'a> { 
    Dereference1ary {set: [&'a Appearance<'a>;1]}, 
    Dereference2ary {set: [&'a Appearance<'a>;2]}, 
} 
impl<'a, 'b> Dereference<'a> { 
    fn set(&self) -> &'b [&'a Appearance<'a>] { 
     match *self { 
      Dereference::Dereference1ary{set} => &set, 
      Dereference::Dereference2ary{set} => &set 
     } 
    } 
} 

fn main() { 
    let r = "hair_color"; 
    let i1 = 42; 
    let i2 = 43; 
    let a1 = Appearance{identity: &i1, role: r}; 
    let a2 = Appearance{identity: &i2, role: r}; 
    let d1 = Dereference::Dereference1ary{set: [&a1]}; 
    let d2 = Dereference::Dereference2ary{set: [&a1, &a2]}; 
    let list: Vec<Dereference> = vec!(d1, d2); 
    println!("{:?}", list); 
    println!("{:?}", d1.set()); 
} 

有一個操場設在這裏：https://play.rust-lang.org/?gist=fd528ebd054a9ce96004c8608166f9ac&version=stable&backtrace=0

Answer 1

的問題是，Derefencece1ary{set}副本set，並採取對副本的引用。你想要的是直接引用set領域，通過使用Dereference1ary{ ref set }

impl<'a> Dereference<'a> { 
    fn set(&self) -> &[&'a Appearance<'a>] { 
     match *self { 
      Dereference::Dereference1ary{ref set} => set, 
      Dereference::Dereference2ary{ref set} => set, 
     } 
    } 
} 

請注意，你的一生01​​是多餘的，但如果你想它明確，你可以寫

fn set<'b>(&'b self) -> &'b [&'a Appearance<'a>] 

，因爲你想借用一部分self對象，所以生命期需要匹配。