rust 迭代器无尽递归title

2024-11-22

给个warning吧至少

昨天写了一点rust, 搓迭代器部分的时候忽生感应，不知道怎么的就这么水灵灵地写成了，没有报错，clippy 和 miri 检查全绿，但是release运行时整个在 from_iter 的时候卡住，单核100%。

做了一个最小复现

#[derive(Debug)]
struct A;

impl A {
    fn new() -> Self {
        Self
    }
}

#[derive(Debug)]
#[allow(dead_code)]
struct V<'a>(&'a Vec<A>);

impl<'a> FromIterator<&'a A> for V<'a> {
    fn from_iter<T: IntoIterator<Item = &'a A>>(iter: T) -> Self {
        iter.into_iter().collect()
    }
}

fn main() {
    let mut b: Vec<A> = Vec::new();
    b.push(A::new());

    let c = V::from_iter(&b);

    println!("{:?}", c);
}

仿佛和rust工具链进行了旷日持久的搏斗，但是对面突然蔫了，然后我一个收不住力 shot my foot。

=> cargo r
   Compiling iter-infrec v0.1.0 (/home/elen/Src/iter-infrec)
    Finished `dev` profile [unoptimized + debuginfo] target(s) in 0.18s
     Running `target/debug/iter-infrec`

thread 'main' has overflowed its stack
fatal runtime error: stack overflow
Aborted (core dumped)

查看调用栈：

Starting program: /home/elen/Src/iter-infrec/target/debug/iter-infrec 
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/nix/store/sl141d1g77wvhr050ah87lcyz2czdxa3-glibc-2.40-36/lib/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
iter_infrec::{impl#1}::from_iter<core::slice::iter::Iter<iter_infrec::A>> (iter=...)
    at src/main.rs:16
16	       iter.into_iter().collect()
(gdb) bt
#0  iter_infrec::{impl#1}::from_iter<core::slice::iter::Iter<iter_infrec::A>> (iter=...)
    at src/main.rs:16
#1  0x0000555555569ed3 in core::iter::traits::iterator::Iterator::collect<core::slice::iter::Iter<iter_infrec::A>, iter_infrec::V> (self=...)
    at /nix/store/49l4vvfi9mi991kfy2wjxmmcx7a1z060-rust-complete-1.84.0-nightly-2024-11-22/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:1971
#2  0x000055555556980e in iter_infrec::{impl#1}::from_iter<core::slice::iter::Iter<iter_infrec::A>> (
    iter=...) at src/main.rs:16
#3  0x0000555555569ed3 in core::iter::traits::iterator::Iterator::collect<core::slice::iter::Iter<iter_infrec::A>, iter_infrec::V> (self=...)
    at /nix/store/49l4vvfi9mi991kfy2wjxmmcx7a1z060-rust-complete-1.84.0-nightly-2024-11-22/lib/rustlib/src/rust/library/core/src/iter/traits/iterator.rs:1971
#4  0x000055555556980e in iter_infrec::{impl#1}::from_iter<core::slice::iter::Iter<iter_infrec::A>> (
    iter=...) at src/main.rs:16

这段代码标黄部分使用了 FromIterator impl 然后其中 collect 的时候调用了自己：

impl<'a> FromIterator<&'a A> for V<'a> {
    fn from_iter<T: IntoIterator<Item = &'a A>>(iter: T) -> Self {
        iter.into_iter().collect()
    }
}

它进行了无止境的递归

但是r-a和clippy之类的linter完全没有给出警告啊。。是相信用户的水平吗

解决方案是


impl<'a> FromIterator<&'a A> for V<'a> {
    fn from_iter<T: IntoIterator<Item = &'a A>>(iter: T) -> Self {
        iter.into_iter().collect()
        let mut m = Vec::new();
        for i in iter.into_iter() {
            m.push(i.0);
        }
        Self(m)
    }
}

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