Question

use std::collections::{HashMap, HashSet};

type Snapshot = HashMap<String, HashSet<String>>;

fn compare_snapshots(snapshot1: Snapshot, snapshot2: Snapshot, entry1: String, entry2: String) {}

fn main() {
    let snapshot1 = HashMap::new();
    let snapshot2 = HashMap::new();

    let entries1: HashSet<String> = snapshot1.keys().cloned().collect();
    let entries2: HashSet<String> = snapshot2.keys().cloned().collect();
    let entries: Vec<String> = entries1.union(&entries2).cloned().collect();

    for e1 in entries {
        for e2 in entries {
            if e1 < e2 {
                compare_snapshots(snapshot1, snapshot2, *e1.to_string(), *e2.to_string());
            }
        }
    }
}

以及以下错误：

error[E0308]: mismatched types
  --> src/main.rs:18:57
   |
18 |                 compare_snapshots(snapshot1, snapshot2, *e1.to_string(), *e2.to_string());
   |                                                         ^^^^^^^^^^^^^^^ expected struct `std::string::String`, found str
   |
   = note: expected type `std::string::String`
              found type `str`

error[E0308]: mismatched types
  --> src/main.rs:18:74
   |
18 |                 compare_snapshots(snapshot1, snapshot2, *e1.to_string(), *e2.to_string());
   |                                                                          ^^^^^^^^^^^^^^^ expected struct `std::string::String`, found str
   |
   = note: expected type `std::string::String`
              found type `str`

鉴于我明确赋予entries一种Vec<String>类型的信息，为什么我得到它们？

Answer 1

您的情况可以减少为

fn repro(_: String) {}

fn main() {
    repro(*"".to_string());
}

由于某种原因，您正在取消引用String。字符串实现了Deref<Target = str>，因此您已明确尝试制作一个str。最终将无法正常工作，因为str的大小不正确，但是您首先遇到的类型不匹配。

删除星号：

fn repro(_: String) {}

fn main() {
    repro("".to_string());
}

另请参阅：

What are Rust's exact auto-dereferencing rules?

预期的字符串类型，当我显式创建字符串时找到类型str

1 个答案: