Why is String::find not a method on &str?

Question

I recently noticed that String::find is actually a method on an owned String.

But I can't see why it wouldn't just be a method on &str instead, making it useful in more cases (and still being just as useful for String). Am I missing a reason for why it's like this, or is it just a historical accident?

Answer 1

显然，文档让你感到困惑。此方法列在本节下面：

因此String甚至没有实现，但实际上只是for &str。

Answer 2

实际上它只适用于String，因为它Deref到str：

Methods from Deref<Target=str>

您在the source for String但未在the source for str中找到它。

Answer 3

实际上......你错了：它不是String方法。

您所关注的是str::find。

就是这样，Rust文档会自动在String页面上包含String实现Deref<Target=str>为can be seen here的事实所带来的方法。

为什么文档中包含可以在Deref目标上调用的方法？

因为您实际上可以直接在String对象上调用它们，因为如果找不到您正在调用的方法，编译器将自动跟随Deref。