中文化时第一次注意到原代码特意把等号对齐：
let empty = Empty;
let null = Null;
中文化后：
// Non-copyable types.
struct 空类;
struct 虚类;
// A trait generic over `类`.
trait 双降类<类> {
// Define a method on the caller type which takes an
// additional single parameter `类` and does nothing with it.
fn 双降(self, _: 类);
}
// Implement `双降类<类1>` for any generic parameter `类1` and
// caller `类2`.
impl<类1, 类2> 双降类<类1> for 类2 {
// This method takes ownership of both passed arguments,
// deallocating both.
fn 双降(self, _: 类1) {}
}
fn main() {
let 空 = 空类;
let 虚 = 虚类;
// Deallocate `空` and `虚`.
空.双降(虚);
//空;
//虚;
// ^ TODO: Try uncommenting these lines.
}
如果放开 空; 这句，报错如下：
error[E0382]: use of moved value: `空`
--> src/main.rs:27:5
|
21 | let 空 = 空类;
| -- move occurs because `空` has type `空类`, which does not implement the `Copy` trait
...
25 | 空.双降(虚);
| -------- `空` moved due to this method call
26 |
27 | 空;
| ^^ value used here after move
|
note: `双降类::双降` takes ownership of the receiver `self`, which moves `空`
--> src/main.rs:9:11
|
9 | fn 双降(self, _: 类);
| ^^^^
For more information about this error, try `rustc --explain E0382`.
如果放开 虚; 这句，报错如下：
error[E0382]: use of moved value: `虚`
--> src/main.rs:28:5
|
22 | let 虚 = 虚类;
| -- move occurs because `虚` has type `虚类`, which does not implement the `Copy` trait
...
25 | 空.双降(虚);
| -- value moved here
...
28 | 虚;
| ^^ value used here after move
|
note: consider changing this parameter type in function `双降` to borrow instead if owning the value isn't necessary
--> src/main.rs:9:20
|
9 | fn 双降(self, _: 类);
| ---- ^^ this parameter takes ownership of the value
| |
| in this function
note: if `虚类` implemented `Clone`, you could clone the value
--> src/main.rs:3:1
|
3 | struct 虚类;
| ^^^^^^^^^^^ consider implementing `Clone` for this type
...
25 | 空.双降(虚);
| -- you could clone this value
For more information about this error, try `rustc --explain E0382`.
空类 和 双降类 没在代码里看到直接关联，居然可以 空.双降 这样调用。暂不补函数的课，继续快进到where再说。
fn 打印机<T: 显示>(t: T) {
println!("{}", t);
}
如直接运行会报错，毕竟还没定义 显示：
error[E0405]: cannot find trait `显示` in this scope
--> src/lib.rs:1:11
|
1 | fn 打印机<类: 显示>(t: 类) {
| ^^^^ not found in this scope
For more information about this error, try `rustc --explain E0405`.
struct S<类: 显示>(类);
// Error! `Vec<T>` does not implement `Display`. This
// specialization will fail.
let s = S(vec![1]);
如期报错如下，好像这几篇头次看到报错信息里带文档链接，但这个反馈信息和泛型有关吗？
error: expected item, found keyword `let`
--> src/lib.rs:5:1
|
5 | let s = S(vec![1]);
| ^^^
| |
| `let` cannot be used for global variables
| help: consider using `static` or `const` instead of `let`
|
= note: for a full list of items that can appear in modules, see <https://doc.rust-lang.org/reference/items.html>
又看到一处对齐：
let rectangle = Rectangle { length: 3.0, height: 4.0 };
let _triangle = Triangle { length: 3.0, height: 4.0 };
这方面还是中文命名有优势些（此文 末条）：
// A trait which implements the print marker: `{:?}`.
use std::fmt::Debug;
trait 求面积 {
fn 面积(&self) -> f64;
}
impl 求面积 for 长方形 {
fn 面积(&self) -> f64 { self.底 * self.高 }
}
#[derive(Debug)]
struct 长方形 { 底: f64, 高: f64 }
#[allow(dead_code)]
struct 三角形 { 底: f64, 高: f64 }
// The generic `调试类` must implement `Debug`. Regardless
// of the type, this will work properly.
fn 调试输出<调试类: Debug>(t: &调试类) {
println!("{:?}", t);
}
// `形状` must implement `求面积`. Any type which meets
// the bound can access `求面积`'s function `面积`.
fn 面积<形状: 求面积>(t: &形状) -> f64 { t.面积() }
fn main() {
let 某长方 = 长方形 { 底: 3.0, 高: 4.0 };
let _某三角 = 三角形 { 底: 3.0, 高: 4.0 };
调试输出(&某长方);
println!("Area: {}", 面积(&某长方));
//调试输出(&_某三角);
//println!("Area: {}", 面积(&_某三角));
// ^ TODO: Try uncommenting these.
// | Error: Does not implement either `Debug` or `求面积`.
}
输出：
长方形 { 底: 3.0, 高: 4.0 }
Area: 12
如果放开 调试输出(&_某三角);，如期报错：
error[E0277]: `三角形` doesn't implement `Debug`
--> src/main.rs:35:10
|
35 | 调试输出(&_某三角);
| -------- ^^^^^^^^ `三角形` cannot be formatted using `{:?}`
| |
| required by a bound introduced by this call
|
= help: the trait `Debug` is not implemented for `三角形`
= note: add `#[derive(Debug)]` to `三角形` or manually `impl Debug for 三角形`
note: required by a bound in `调试输出`
--> src/main.rs:20:14
|
20 | fn 调试输出<调试类: Debug>(t: &调试类) {
| ^^^^^ required by this bound in `调试输出`
help: consider annotating `三角形` with `#[derive(Debug)]`
|
16 + #[derive(Debug)]
17 | struct 三角形 { 底: f64, 高: f64 }
|
For more information about this error, try `rustc --explain E0277`.
在 struct 前加一句：
#[derive(Debug)]
struct 三角形 { 底: f64, 高: f64 }
输出正确：
长方形 { 底: 3.0, 高: 4.0 }
Area: 12
三角形 { 底: 3.0, 高: 4.0 }
再放开末句 println!("Area: {}", 面积(&_某三角));，报错如下：
error[E0277]: the trait bound `三角形: 求面积` is not satisfied
--> src/main.rs:36:29
|
36 | println!("Area: {}", 面积(&_某三角));
| ---- ^^^^^^^^ the trait `求面积` is not implemented for `三角形`
| |
| required by a bound introduced by this call
|
= help: the trait `求面积` is implemented for `长方形`
note: required by a bound in `面积`
--> src/main.rs:26:11
|
26 | fn 面积<形状: 求面积>(t: &形状) -> f64 { t.面积() }
| ^^^^^^ required by this bound in `面积`
For more information about this error, try `rustc --explain E0277`.
按help提示，参考长方形实现所需trait：
impl 求面积 for 三角形 {
fn 面积(&self) -> f64 { self.底 * self.高 / 2 }
}
报错：
error[E0277]: cannot divide `f64` by `{integer}`
--> src/main.rs:13:43
|
13 | fn 面积(&self) -> f64 { self.底 * self.高 / 2 }
| ^ no implementation for `f64 / {integer}`
|
= help: the trait `Div<{integer}>` is not implemented for `f64`
= help: the following other types implement trait `Div<Rhs>`:
`&f64` implements `Div<f64>`
`&f64` implements `Div`
`f64` implements `Div<&f64>`
`f64` implements `Div`
help: consider using a floating-point literal by writing it with `.0`
|
13 | fn 面积(&self) -> f64 { self.底 * self.高 / 2.0 }
| ++
For more information about this error, try `rustc --explain E0277`.
按提示改为 / 2.0，输出正确：
长方形 { 底: 3.0, 高: 4.0 }
Area: 12
三角形 { 底: 3.0, 高: 4.0 }
Area: 6
发现 Display 也在标准库。
use std::fmt::{Debug, Display};
fn 比较输出<T: Debug + Display>(t: &T) {
println!("Debug: `{:?}`", t);
println!("Display: `{}`", t);
}
fn 比较类型<T: Debug, U: Debug>(t: &T, u: &U) {
println!("t: `{:?}`", t);
println!("u: `{:?}`", u);
}
fn main() {
let 文字 = "words";
let 数组 = [1, 2, 3];
let 矢量 = vec![1, 2, 3];
比较输出(&文字);
//比较输出(&数组);
// TODO ^ Try uncommenting this.
比较类型(&数组, &矢量);
}
运行输出：
Debug: `"words"`
Display: `words`
t: `[1, 2, 3]`
u: `[1, 2, 3]`
放开 比较输出(&数组); 报错如下：
error[E0277]: `[{integer}; 3]` doesn't implement `std::fmt::Display`
--> src/main.rs:19:10
|
19 | 比较输出(&数组);
| -------- ^^^^^ `[{integer}; 3]` cannot be formatted with the default formatter
| |
| required by a bound introduced by this call
|
= help: the trait `std::fmt::Display` is not implemented for `[{integer}; 3]`
= note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
note: required by a bound in `比较输出`
--> src/main.rs:3:20
|
3 | fn 比较输出<T: Debug + Display>(t: &T) {
| ^^^^^^^ required by this bound in `比较输出`
For more information about this error, try `rustc --explain E0277`.
注意到反馈里用 [{integer}; 3] 表达长度为3的整数数组。
试了这么写 let 数组: [{integer}; 3] = [1, 2, 3]; 报错如下：
error: expected type, found `{`
--> src/main.rs:15:14
|
15 | let 数组: [{integer}; 3] = [1, 2, 3];
| - ^ expected type
| |
| while parsing the type for `数组`
| help: use `=` if you meant to assign
error[E0425]: cannot find value `integer` in this scope
--> src/main.rs:15:15
|
15 | let 数组: [{integer}; 3] = [1, 2, 3];
| ^^^^^^^ not found in this scope
error[E0070]: invalid left-hand side of assignment
--> src/main.rs:15:28
|
15 | let 数组: [{integer}; 3] = [1, 2, 3];
| -------------- ^
| |
| cannot assign to this expression
Some errors have detailed explanations: E0070, E0425.
For more information about an error, try `rustc --explain E0070`.
不知在代码中如何指定“长度为3的整数数组”这一类型。理想中反馈信息中使用的语法应尽可能与代码一致。