<code>CharPos</code>类型没有<code>to_usize</code>方法。但是提示也给出了，<code>CharPos</code>实现了<code>Pos</code> trait，这个trait提供了<code>to_usize</code>方法。你需要将这个trait引入到当前作用域才能使用它的方法。
<img src="https://cdn.hashnode.com/res/hashnode/image/upload/v1691729789147/fe8cbe00-87cf-4406-bcd0-81a486314aae.png" alt class="image--center mx-auto" />
<pre><code class="lang-rust">error[E0599]: no method named `to_usize` found for struct `CharPos` in the current scope
 --&gt; src/ptr_provenance.rs:1769:81
 |
1769 | ... location.file.name, location.line, location.col.to_usize() + 1
 | ^^^^^^^^ method not found in `CharPos`
 |
 = help: items from traits can only be used if the trait is in scope
 = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
 `use crate::rustc_span::Pos;`

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0599`.
</code></pre>

`CharPos`类型没有`to_usize`方法。但是提示也给出了，`CharPos`实现了`Pos` trait，这个trait提供了`to_usize`方法。你需要将这个trait引入到当前作用域才能使用它的方法。

![](https://cdn.hashnode.com/res/hashnode/image/upload/v1691729789147/fe8cbe00-87cf-4406-bcd0-81a486314aae.png align="center")

```rust
error[E0599]: no method named `to_usize` found for struct `CharPos` in the current scope
    --> src/ptr_provenance.rs:1769:81
     |
1769 | ...                   location.file.name, location.line, location.col.to_usize() + 1
     |                                                                       ^^^^^^^^ method not found in `CharPos`
     |
     = help: items from traits can only be used if the trait is in scope
     = note: the following trait is implemented but not in scope; perhaps add a `use` for it:
             `use crate::rustc_span::Pos;`

error: aborting due to previous error; 1 warning emitted

For more information about this error, try `rustc --explain E0599`.
```

rustc_span::CharPos实现了Pos trait，这个trait提供了to_usize方法。需要将这个trait引入到当前作用域才能使用该方法。