如何制作动态索引以获取元组的值? [英] How do I make a dynamic index to get the value of a tuple?

问题描述

在 Python 中，我了解到可以通过动态索引检索元组值:

In Python, I learned that I can retrieve a tuple value by a dynamic index:

data = (1,2,3,4)
data[0]

for a in range(len(data)):
   print(data[a])

输出:

1
2
3
4

如何在 Rust 中做到这一点?

how to do this in Rust?

我尝试过这样的事情:

fn main() {
    let data = (12, 3, 4, 5);
    for a in 0..100 {
        println!("{}", data.a);
    }
}

但它不起作用，它只会给我一些错误.

But it's not working, it only gives me some error.

推荐答案

正如其他人指出的那样，您可能想要使用数组或 Vec 代替.

As others pointed out, you probably want to use an array or Vec<T> instead.

正如本书所解释的，元组是异构数据类型:每个元组元素可以有不同的类型.如果您可以遍历所有元组值，可能会发生奇怪的事情:

As the book explains, tuples are heterogeneous data types: each tuple element can have a different type. If you could iterate over all tuple values, strange things could happen:

let data = (12, true);
for a in 0..data.len() {
    // Oops: `+ 1` makes sense for the integer, but not for the bool
    println!("{}", data.a + 1); 
}

另一方面，数组是同构类型:所有元素都具有相同的类型！所以上面的代码片段中的问题不会发生.Vec 也是如此:只能存储 T 类型的元素.Vec 和数组的区别:向量可以增长，即动态调整大小，而数组在编译时具有固定大小.

On the other hand, arrays are homogeneous types: all elements have the same type! So the problem in the snippet above can't occur. The same is true for Vec<T>: only elements of type T can be stored. The difference between Vec<T> and an array: a vector can grow, i.e. is dynamically sized while an array has a fixed size at compile time.

这是带有数组的代码片段(游乐场):

Here is your code snippet with an array (Playground):

let data = [12, 3, 4, 5];
for a in 0..data.len() {
    println!("{}", data[a]);
}

当然，如果你愿意，你可以迭代数组之类的集合而不迭代索引(例如 for elem in &data).

But of course, you can iterate over collections like arrays without iterating over indices, if you want (e.g. for elem in &data).

最后一点:当然，在技术上可以通过执行 unsafe 指针魔术来创建动态元组索引 - 假设您只在元组中存储相同的类型.但这几乎没有必要，应该避免.这就是为什么我什至不会展示代码如何做到这一点.

As a last note: of course, it's technically possible to create a dynamic tuple index by doing unsafe pointer magic – assuming you only store the same types in your tuple. But this is hardly ever necessary and should be avoided. That's why I won't even show code how to do it.

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