Rust 如何知道需要或提供哪些 trait 方法? [英] How does Rust know which trait methods are required or provided?

问题描述

来自 std::iter::Iterator 文档，可以看到只需要next 方法:

所需方法

fn next(&mut self) -> Option<Self::Item>

但来自源代码，删除评论后:

pub trait Iterator {
    /// The type of the elements being iterated over.
    #[stable(feature = "rust1", since = "1.0.0")]
    type Item;
    ......
    #[stable(feature = "rust1", since = "1.0.0")]
    fn next(&mut self) -> Option<Self::Item>;
    ......
    #[inline]
    #[stable(feature = "rust1", since = "1.0.0")]
    fn size_hint(&self) -> (usize, Option<usize>) { (0, None) }
    ......
}

我可以看到，除了 #[inline] 属性之外，必需方法和提供方法之间没有区别.Rust 如何知道需要或提供哪种方法?

I can see, except for the #[inline] attribute, there is no difference between required and provided methods. How does Rust know which method is required or provided?

推荐答案

它相当简单:提供的(可选)函数有一个默认实现，而不是必需的.

It is rather simple: the provided (optional) functions have a default implementation, not the required.

请注意，如果您愿意，您可以重新实现提供的函数，以便它可以比特定结构/枚举的默认函数执行得更好.

Note that you can re-implement the provided functions if you wish so it can perform better than the default one for your particular struct/enum.

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