我在初始化固定长度数组时遇到麻烦。 My attempts so far all result in the same "use of possibly uninitialized variable: foo_array
" error:
#[derive(Debug)]
struct Foo { a: u32, b: u32 }
impl Default for Foo {
fn default() -> Foo { Foo{a:1, b:2} }
}
pub fn main() {
let mut foo_array: [Foo; 10];
// Do something here to in-place initialize foo_array?
for f in foo_array.iter() {
println!("{:?}", f);
}
}
error[E0381]: use of possibly uninitialized variable: `foo_array`
--> src/main.rs:13:14
|
13 | for f in foo_array.iter() {
| ^^^^^^^^^ use of possibly uninitialized `foo_array`
我实现了
Default
特性,但是默认情况下,Rust似乎没有像C++构造函数那样调用它。初始化固定长度数组的正确方法是什么?我想进行高效的就地初始化,而不是某种复制。
相关:Why is the Copy trait needed for default (struct valued) array initialization?
相关:Is there a way to not have to initialize arrays twice?
最佳答案
安全但somewhat inefficient solution:
#[derive(Copy, Clone, Debug)]
struct Foo {
a: u32,
b: u32,
}
fn main() {
let mut foo_array = [Foo { a: 10, b: 10 }; 10];
}
由于您专门要求a solution without copies:
use std::mem::MaybeUninit;
#[derive(Debug)]
struct Foo {
a: u32,
b: u32,
}
// We're just implementing Drop to prove there are no unnecessary copies.
impl Drop for Foo {
fn drop(&mut self) {
println!("Destructor running for a Foo");
}
}
pub fn main() {
let array = {
// Create an array of uninitialized values.
let mut array: [MaybeUninit<Foo>; 10] = unsafe { MaybeUninit::uninit().assume_init() };
for (i, element) in array.iter_mut().enumerate() {
let foo = Foo { a: i as u32, b: 0 };
*element = MaybeUninit::new(foo);
}
unsafe { std::mem::transmute::<_, [Foo; 10]>(array) }
};
for element in array.iter() {
println!("{:?}", element);
}
}
这是the documentation of
MaybeUninit
推荐的。