Vec为什么不实现Iterator特性？

Question

Vec不实现该Iterator特性的设计原因是什么？必须始终调用iter()所有向量和切片将使代码行更长。

例：

let rx = xs.iter().zip(ys.iter());

与Scala相比：

val rx = xs.zip(ys)

Answer 1

An iterator has an iteration state. It must know what will be the next element to give you.

So a vector by itself isn't an iterator, and the distinction is important. You can have two iterators over the same vector, for example, each with its specific iteration state.

But a vector can provide you an iterator, that's why it implements IntoIterator, which lets you write this:

let v = vec![1, 4];
for a in v {
    dbg!(a);
}

Many functions take an IntoIterator when an iterator is needed, and that's the case for zip, which is why

let rx = xs.iter().zip(ys.iter());

can be replaced with

let rx = xs.iter().zip(ys);

Answer 2

Vec不实现Iteratortrait的设计原因是什么？

它应该实现三个迭代器中的哪一个？您可以从 a 获得三种不同类型的迭代器Vec：

1. vec.iter()给Iterator<Item = &T>,
2. vec.iter_mut()给出Iterator<Item = &mut T>并修改向量和
3. vec.into_iter()Iterator<Item = T>在这个过程中给出和消耗向量。

与 Scala 相比：

在 Scala 中它也不Iterator直接实现，因为Iterator需要向量本身没有的下一项指针。然而，由于 Scala 没有移动语义，它只有一种从向量创建迭代器的方法，所以它可以隐式地进行转换。Rust 有三种方法，所以它必须问你想要哪一种。