为什么`FromIterator`的实现使用`IntoIterator`而不是`Iterator`? [英] Why does the implementation of `FromIterator` use an `IntoIterator` instead of an `Iterator`?

问题描述

Rust文档中的FromIterator特征的示例实现是:

The example implementation of the FromIterator trait in the Rust docs is:

impl FromIterator<i32> for MyCollection {
    fn from_iter<I: IntoIterator<Item=i32>>(iter: I) -> Self {
        let mut c = MyCollection::new();

        for i in iter {
            c.add(i);
        }

        c
    }
}

FromIterator定义如何从迭代器创建类型. from_iter的签名需要一个实现IntoIterator的类型，该类型定义了如何将类型转换为Iterator.

FromIterator defines how a type will be created from an iterator. The signature of from_iter requires a type that implements IntoIterator, which defines how a type may be converted into an Iterator.

from_iter是这样定义的，因为IntoIterator的要求不像Iterator一样严格吗?

Is from_iter defined this way because IntoIterator is not as strict a requirement as Iterator?

推荐答案

from_iter是这样定义的，因为IntoIterator的要求不像Iterator一样严格吗?

Is from_iter defined this way because IntoIterator is not as strict a requirement as Iterator?

是的

IntoIterator是为Iterator自动实现的，因此实现IntoIterator的类型集是实现Iterator的那些类型的超集.

IntoIterator is automatically implemented for Iterator, therefore the set of types implementing IntoIterator is a superset of those implementing Iterator.

制作通用函数时，最好将其需求降到最低，即，使其尽可能通用.

When crafting a generic function, it's good to minimize its requirements, i.e., make it as generic as possible.

当然，需要在以下两者之间进行权衡:

Of course, there's a trade-off between:

• 易用性:适用于尽可能多的类型，
• 易于实施.

• ease of use: works with as many types as possible,
• ease of implementation.

对于孤立代码库中的一个单独功能，可能不值得在易用性上进行大量优化.对于标准库中的特征/功能，由于用户数量远远超过了(此特定产品的)开发人员的数量，因此，折衷方案强烈支持易用性.

For a lone function in your isolated codebase, it may not be worth optimizing for ease-of-use much; for a trait/function in the standard library, since the number of users far outweigh the number of developers (of this particular piece), the trade-off is strongly in favor of ease-of-use.

由于从IntoIterator转到Iterator非常简单，因此对实现没有太大影响，因此很容易进行调用.

And since going from IntoIterator to Iterator is so simple, and thus doesn't weigh much on the implementation, it's an easy call to make.

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