rust - 数字数组(不是 Vec)的类型是什么？

Question

我无法确定数组的正确类型(不是 Vec)。以下代码无法编译:

fn sum(a: [f32]) -> f32 {
    return 3.0;
}

fn main() {
    let x = [0.0, 1.0, 2.0];
    print!("{}\n", sum(x));
}

error[E0277]: the trait bound `[f32]: std::marker::Sized` is not satisfied
 --> src/main.rs:1:8
  |
1 | fn sum(a: [f32]) -> f32 {
  |        ^ `[f32]` does not have a constant size known at compile-time
  |
  = help: the trait `std::marker::Sized` is not implemented for `[f32]`
  = note: all local variables must have a statically known size

error[E0308]: mismatched types
 --> src/main.rs:7:24
  |
7 |     print!("{}\n", sum(x));
  |                        ^ expected slice, found array of 3 elements
  |
  = note: expected type `[f32]`
             found type `[{float}; 3]`

sum 中a 的合适类型是什么？

Answer 1

数组的类型是[ElementType;长度]

• [i32; 10]
• [字符； 16]
• [u8; 3]
• [字符串； 5]

令人惊讶的是，这并没有在 The Rust Programming Language 中直接调用, 除了在 operators and symbols appendix .要使它有用，您必须已经知道所需的语法!

但是，编译器确实会引导您找到正确的解决方案。花时间完整阅读 Rust 编译器的错误消息。它们通常非常好，而且大多数都付出了很多努力。查看错误中的注释；它告诉你你有什么类型:

  = note: expected type `[f32]`
             found type `[{float}; 3]`

found type `[{float}; 3]`

您也可以print out the type of a variable :

let x: () = [0.0, 1.0, 2.0];

针对您的特定功能的修复:

fn sum(a: [f32; 3]) -> f32 {
    3.0
}

另见:

• What is the {integer} or {float} in a compiler error message?
• How do I create a type alias for an array of char with a fixed size?
• Passing array to function: array must have 'Sized' type
• How to define a function with a generic fixed-length array?
• How do I print the type of a variable in Rust?