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mir.txt

// WARNING: This output format is intended for human consumers only
// and is subject to change without notice. Knock yourself out.
static <impl at <anon>:11:1: 33:2>::display::__STATIC_FMTSTR: &[&str] = {
    let mut _0: &[&str];                 // return pointer
    let mut _1: &[&str; 2];
    let mut _2: &[&str; 2];
    let mut _3: [&str; 2];

    bb0: {
        _3 = [const "", const "\n"];     // scope 0 at <println macros>:3:18: 3:43
        _2 = &_3;                        // scope 0 at <println macros>:3:18: 3:43
        _1 = _2;                         // scope 0 at <println macros>:3:18: 3:43
        _0 = _1 as &[&str] (Unsize);     // scope 0 at <println macros>:3:18: 3:43
        return;                          // scope 0 at <println macros>:3:18: 3:43
    }
}

fn <impl at <anon>:11:1: 33:2>::bar(_1: &mut Hoge) -> &str {
    let mut _0: &str;                    // return pointer
    scope 1 {
        let _2: &mut Hoge;               // "self" in scope 1 at <anon>:25:16: 25:28
    }

    bb0: {
        StorageLive(_2);                 // scope 0 at <anon>:25:16: 25:28
        _2 = _1;                         // scope 0 at <anon>:25:16: 25:28
        _0 = ((*_2).0: &str);            // scope 1 at <anon>:26:9: 26:18
        StorageDead(_2);                 // scope 0 at <anon>:27:6: 27:6
        return;                          // scope 1 at <anon>:27:6: 27:6
    }
}

fn <impl at <anon>:11:1: 33:2>::new(_1: &str) -> Hoge {
    let mut _0: Hoge;                    // return pointer
    scope 1 {
        let _2: &str;                    // "s" in scope 1 at <anon>:12:12: 12:13
    }
    let mut _3: &str;

    bb0: {
        StorageLive(_2);                 // scope 0 at <anon>:12:12: 12:13
        _2 = _1;                         // scope 0 at <anon>:12:12: 12:13
        StorageLive(_3);                 // scope 1 at <anon>:13:22: 13:23
        _3 = _2;                         // scope 1 at <anon>:13:22: 13:23
        _0 = Hoge { hoge: _3 };          // scope 1 at <anon>:13:9: 13:25
        StorageDead(_3);                 // scope 1 at <anon>:13:25: 13:25
        StorageDead(_2);                 // scope 0 at <anon>:14:6: 14:6
        return;                          // scope 1 at <anon>:14:6: 14:6
    }
}

fn main() -> () {
    let mut _0: ();                      // return pointer
    scope 1 {
        let _1: std::string::String;     // "s" in scope 1 at <anon>:54:13: 54:14
        scope 2 {
            let mut _4: Hoge;            // "hoge" in scope 2 at <anon>:55:13: 55:21
            scope 3 {
                let _9: &str;            // "_borrow" in scope 3 at <anon>:56:13: 56:20
            }
        }
    }
    let mut _2: &str;
    let mut _3: &str;
    let mut _5: &str;
    let mut _6: &str;
    let mut _7: &std::string::String;
    let mut _8: &std::string::String;
    let mut _10: &mut Hoge;
    let mut _11: ();
    let mut _12: &Hoge;

    bb0: {
        StorageLive(_1);                 // scope 0 at <anon>:54:13: 54:14
        StorageLive(_2);                 // scope 0 at <anon>:54:17: 54:23
        StorageLive(_3);                 // scope 0 at <anon>:54:17: 54:23
        _3 = const "TEST";               // scope 0 at <anon>:54:17: 54:23
        _2 = _3;                         // scope 0 at <anon>:54:17: 54:23
        _1 = const std::borrow::ToOwned::to_owned(_2) -> bb1; // scope 0 at <anon>:54:17: 54:34
    }

    bb1: {
        StorageDead(_2);                 // scope 0 at <anon>:54:34: 54:34
        StorageDead(_3);                 // scope 0 at <anon>:54:35: 54:35
        StorageLive(_4);                 // scope 1 at <anon>:55:13: 55:21
        StorageLive(_5);                 // scope 1 at <anon>:55:34: 55:36
        StorageLive(_6);                 // scope 1 at <anon>:55:34: 55:36
        StorageLive(_7);                 // scope 1 at <anon>:55:34: 55:36
        StorageLive(_8);                 // scope 1 at <anon>:55:34: 55:36
        _8 = &_1;                        // scope 1 at <anon>:55:34: 55:36
        _7 = _8;                         // scope 1 at <anon>:55:34: 55:36
        _6 = const std::ops::Deref::deref(_7) -> [return: bb4, unwind: bb3]; // scope 1 at <anon>:55:34: 55:36
    }

    bb2: {
        resume;                          // scope 0 at <anon>:35:1: 65:2
    }

    bb3: {
        drop(_1) -> bb2;                 // scope 0 at <anon>:58:6: 58:6
    }

    bb4: {
        _5 = _6;                         // scope 1 at <anon>:55:34: 55:36
        StorageDead(_7);                 // scope 1 at <anon>:55:36: 55:36
        _4 = const Hoge::new(_5) -> [return: bb5, unwind: bb3]; // scope 1 at <anon>:55:24: 55:37
    }

    bb5: {
        StorageDead(_5);                 // scope 1 at <anon>:55:37: 55:37
        StorageDead(_6);                 // scope 1 at <anon>:55:38: 55:38
        StorageDead(_8);                 // scope 1 at <anon>:55:38: 55:38
        StorageLive(_9);                 // scope 2 at <anon>:56:13: 56:20
        StorageLive(_10);                // scope 2 at <anon>:56:23: 56:27
        _10 = &mut _4;                   // scope 2 at <anon>:56:23: 56:27
        _9 = const Hoge::baz(_10) -> [return: bb6, unwind: bb3]; // scope 2 at <anon>:56:23: 56:33
    }

    bb6: {
        StorageDead(_10);                // scope 2 at <anon>:56:33: 56:33
        StorageLive(_12);                // scope 3 at <anon>:57:9: 57:13
        _12 = &_4;                       // scope 3 at <anon>:57:9: 57:13
        _11 = const Hoge::display(_12) -> [return: bb7, unwind: bb3]; // scope 3 at <anon>:57:9: 57:23
    }

    bb7: {
        StorageDead(_12);                // scope 3 at <anon>:57:23: 57:23
        _0 = ();                         // scope 3 at <anon>:53:5: 58:6
        StorageDead(_9);                 // scope 2 at <anon>:58:6: 58:6
        StorageDead(_4);                 // scope 1 at <anon>:58:6: 58:6
        drop(_1) -> bb8;                 // scope 0 at <anon>:58:6: 58:6
    }

    bb8: {
        StorageDead(_1);                 // scope 0 at <anon>:58:6: 58:6
        return;                          // scope 0 at <anon>:65:2: 65:2
    }
}

fn <impl at <anon>:11:1: 33:2>::foo(_1: &mut Hoge) -> &str {
    let mut _0: &str;                    // return pointer
    scope 1 {
        let _2: &mut Hoge;               // "self" in scope 1 at <anon>:20:12: 20:24
    }
    let mut _3: &str;

    bb0: {
        StorageLive(_2);                 // scope 0 at <anon>:20:12: 20:24
        _2 = _1;                         // scope 0 at <anon>:20:12: 20:24
        StorageLive(_3);                 // scope 1 at <anon>:21:9: 21:18
        _3 = ((*_2).0: &str);            // scope 1 at <anon>:21:9: 21:18
        _0 = _3;                         // scope 1 at <anon>:21:9: 21:18
        StorageDead(_3);                 // scope 1 at <anon>:21:18: 21:18
        StorageDead(_2);                 // scope 0 at <anon>:22:6: 22:6
        return;                          // scope 1 at <anon>:22:6: 22:6
    }
}

fn <impl at <anon>:11:1: 33:2>::baz(_1: &mut Hoge) -> &str {
    let mut _0: &str;                    // return pointer
    scope 1 {
        let _2: &mut Hoge;               // "self" in scope 1 at <anon>:30:16: 30:28
    }
    let mut _3: &str;

    bb0: {
        StorageLive(_2);                 // scope 0 at <anon>:30:16: 30:28
        _2 = _1;                         // scope 0 at <anon>:30:16: 30:28
        StorageLive(_3);                 // scope 1 at <anon>:31:9: 31:18
        _3 = ((*_2).0: &str);            // scope 1 at <anon>:31:9: 31:18
        _0 = _3;                         // scope 1 at <anon>:31:9: 31:18
        StorageDead(_3);                 // scope 1 at <anon>:31:18: 31:18
        StorageDead(_2);                 // scope 0 at <anon>:32:6: 32:6
        return;                          // scope 1 at <anon>:32:6: 32:6
    }
}

fn <impl at <anon>:11:1: 33:2>::display(_1: &Hoge) -> () {
    let mut _0: ();                      // return pointer
    scope 1 {
        let _2: &Hoge;                   // "self" in scope 1 at <anon>:15:16: 15:21
        scope 2 {
            let _11: &&str;              // "__arg0" in scope 2 at <anon>:1:1: 1:1
        }
    }
    let mut _3: std::fmt::Arguments;
    let mut _4: &[&str];
    let mut _5: &[std::fmt::ArgumentV1];
    let mut _6: &[std::fmt::ArgumentV1; 1];
    let mut _7: &[std::fmt::ArgumentV1; 1];
    let mut _8: [std::fmt::ArgumentV1; 1];
    let mut _9: (&&str,);
    let mut _10: &&str;
    let mut _12: std::fmt::ArgumentV1;
    let mut _13: &&str;
    let mut _14: fn(&&str, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error>;

    bb0: {
        StorageLive(_2);                 // scope 0 at <anon>:15:16: 15:21
        _2 = _1;                         // scope 0 at <anon>:15:16: 15:21
        StorageLive(_3);                 // scope 1 at <print macros>:2:27: 2:58
        StorageLive(_4);                 // scope 1 at <println macros>:3:18: 3:43
        _4 = (Hoge::display::__STATIC_FMTSTR: &[&str]); // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_5);                 // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_6);                 // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_7);                 // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_8);                 // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_9);                 // scope 1 at <println macros>:3:18: 3:43
        StorageLive(_10);                // scope 1 at <anon>:16:24: 16:33
        _10 = &((*_2).0: &str);          // scope 1 at <anon>:16:24: 16:33
        _9 = (_10,);                     // scope 1 at <println macros>:3:18: 3:43
        StorageDead(_10);                // scope 1 at <println macros>:3:43: 3:43
        StorageLive(_11);                // scope 1 at <anon>:1:1: 1:1
        _11 = (_9.0: &&str);             // scope 1 at <anon>:1:1: 1:1
        StorageLive(_12);                // scope 2 at <print macros>:2:27: 2:58
        StorageLive(_13);                // scope 2 at <anon>:16:24: 16:33
        _13 = _11;                       // scope 2 at <anon>:16:24: 16:33
        StorageLive(_14);                // scope 2 at <anon>:16:24: 16:33
        _14 = const std::fmt::Display::fmt as fn(&&str, &mut std::fmt::Formatter<'_>) -> std::result::Result<(), std::fmt::Error> (ReifyFnPointer); // scope 2 at <anon>:16:24: 16:33
        _12 = const std::fmt::ArgumentV1::new(_13, _14) -> bb1; // scope 2 at <print macros>:2:27: 2:58
    }

    bb1: {
        StorageDead(_14);                // scope 2 at <print macros>:2:58: 2:58
        StorageDead(_13);                // scope 2 at <print macros>:2:58: 2:58
        _8 = [_12];                      // scope 2 at <println macros>:3:18: 3:43
        StorageDead(_12);                // scope 2 at <println macros>:3:43: 3:43
        StorageDead(_11);                // scope 1 at <println macros>:3:43: 3:43
        _7 = &_8;                        // scope 1 at <println macros>:3:18: 3:43
        _6 = _7;                         // scope 1 at <println macros>:3:18: 3:43
        _5 = _6 as &[std::fmt::ArgumentV1] (Unsize); // scope 1 at <println macros>:3:18: 3:43
        StorageDead(_6);                 // scope 1 at <println macros>:3:43: 3:43
        _3 = const std::fmt::Arguments::new_v1(_4, _5) -> bb2; // scope 1 at <print macros>:2:27: 2:58
    }

    bb2: {
        StorageDead(_5);                 // scope 1 at <print macros>:2:58: 2:58
        StorageDead(_4);                 // scope 1 at <print macros>:2:58: 2:58
        _0 = const std::io::_print(_3) -> bb3; // scope 1 at <print macros>:2:1: 2:60
    }

    bb3: {
        StorageDead(_3);                 // scope 1 at <print macros>:2:60: 2:60
        StorageDead(_7);                 // scope 1 at <anon>:17:6: 17:6
        StorageDead(_8);                 // scope 1 at <anon>:17:6: 17:6
        StorageDead(_9);                 // scope 1 at <anon>:17:6: 17:6
        StorageDead(_2);                 // scope 0 at <anon>:17:6: 17:6
        return;                          // scope 1 at <anon>:17:6: 17:6
    }
}

playground.rs

#![allow(dead_code)]

// ※主な変更点
// 1. foo(), bar() の第一引数を &self から &mut self に変更
// 2. baz() を追加

struct Hoge<'s> {
    hoge: &'s str,
}

impl<'s> Hoge<'s> {
    fn new(s: &'s str) -> Hoge<'s> {
        Hoge { hoge: s }
    }
    fn display(&self) {
        println!("{}", self.hoge)
    }

    // (1) &mut self, &self.hoge の lifetime が 's の場合
    fn foo(&'s mut self) -> &'s str {
        self.hoge
    }

    // (2) &mut self, &self.hoge の lifetime をパラメータにとる場合
    fn bar<'f>(&'f mut self) -> &'f str {
        self.hoge
    }

    // (3) &mut self の lifetime のみをパラメータにとる場合
    fn baz<'f>(&'f mut self) -> &'s str {
        self.hoge
    }
}

fn main() {
    // (1') foo()
    /* {
        let s = "TEST".to_owned();
        let mut hoge = Hoge::new(&s);
        let _borrow = hoge.foo();
        hoge.display();
    } */

    // (2') bar()
    /* {
        let s = "TEST".to_owned();
        let mut hoge = Hoge::new(&s);
        let _borrow = hoge.bar();
        hoge.display();
    } */

    // (3') baz()
    {
        let s = "TEST".to_owned();
        let mut hoge = Hoge::new(&s);
        let _borrow = hoge.baz();
        hoge.display();
    }

    // (1'), (2') は borrow checker により弾かれてコンパイルに失敗する
    // ※ hoge.display() を呼び出す際，その前に読んだ時の mutable な借用が解放されていないと言われる

    // (3') では borrow checker によるチェックをパスする
    // ※ hoge.display() の呼び出し時には baz() で作られた &mut hoge が開放済みになる
}