ライフタイム

code:.rs

{

let r; // ---------+-- 'a

// |

{ // |

let x = 5; // -+-- 'b |

r = &x; // | |

} // -+ |

// |

println!("r: {}", r); // |

} // ---------+

code:.rs

fn longest(x: &str, y: &str) -> &str { // コンパイル不可

if x.len() > y.len() {

x

} else {

y

}

}

code:.rs

fn longest<'a>(x: &'a str, y: &'a str) -> &'a str {

if x.len() > y.len() {

x

} else {

y

}

}

code:.rs

fn main() {

let string1 = String::from("long string is long");

let result;

{

let string2 = String::from("xyz");

result = longest(string1.as_str(), string2.as_str());

// ↑ borrowed value does not live long enough

}

println!("The longest string is {}", result);

}