问题
I'm currently confused by [T] and &[T] in Rust. Let's start by what I know:
[T; n]is an array of n elements,&[T; n]is a pointer to an array with n elements,[T]is unsized and points to sequence of elementsT, while&[T]is a sized fat pointer and points to a sequence of elementsT.
My confusion starts with the naming convention of the two items. From the documentation of Rust, they provide the following example:
let a: [i32; 5] = [1, 2, 3, 4, 5]; // An array of type [T, n]
let slice: &[i32] = &a[1..3]; // A slice of type &[T]
and states
This slice has the type &[i32].
So, I assume &[T] is called a slice. What's the name of the item [T] so ? What is the usage of [T] exactly ? You can't embed it into a struct (it's unsized), you can't take this type in parameter for the same reason. I can't figure out a practical usage of it.
Thanks!
回答1:
What's the name of the item
[T]so ? What is the usage of[T]exactly ?
[T] is a block of contiguous memory, filled with items of type T. It is rarely referred to by name directly because it needs to be behind a pointer to be useful. That is usually a &[T], commonly referred to as a slice, but could also be other pointer types.
The term "slice" is overloaded, but it is not usually a cause of confusion since it really doesn't come up much. In general, if the word "slice" is used by itself then it means &[T]. If it has some other modifier, then it probably refers to a different pointer type. For example Box<[T]> is a "boxed slice" and Rc<[T]> might be called a "ref-counted slice".
回答2:
Regarding slices:
E.g. string literals are slices of type &str. But slices of Strings (of type String) are also of type &str such as slice: &str = &String [0..n-1].
Furthermore, slice: &[T] in:
Arrays like
array: [T; n]- if you want a piece of it, you can take aslice = &array [1..n-1]which means that slice is of type &[T].Vectors such as
vector: Vec<T>you can take a part of it as a slice: &[T].
来源：https://stackoverflow.com/questions/57808948/confusion-between-t-and-t