letx;foobar(x);// error: borrow of possibly-uninitialized variable: `x` x = 42; 然而,这样做完全没问题: 代码语言:javascript 复制 letx;x=42;foobar(x);// the type of `x` will be inferred from here 下划线表示特殊的命名,或者更确切地说是「缺失的命名」,它和 Python 的用法有点像: 代码...
rustc_hir::Ty has generics and lifetimes; however, some of those lifetimes are special markers like LifetimeName::Implicit. ty::Ty has the full type, including generics and lifetimes, even if the user left them out fn foo(x: u32) → u32 { } - Two rustc_hir::Ty representing each...
Running 'target/debug/ch1-fruit' thread 'main' panicked at 'index out of bounds: the len is 3 but the index is 4', src/main.rs:3:25 note: run with 'RUST_BACKTRACE=1' environment variable to display a backtrace 清单1.6所示的是一个迭代器失效的例子。也就是说,在迭代过程中,因迭代器中...
很不幸,这段代码同样无法编译通过,错误是: error[E0384]: cannot assign twice to immutable variable `x` --> test-own1.rs:3:5 | 2 | let x=5; | - | | | first assignment to `x` | help: make this binding mutable: `mut x` 3 | x = x+1; | ^^^ cannot assign twice to immuta...
error[E0384]: cannot assign twice to immutable variable `x` --> src/main.rs:4:5 | 2 | let x = 5; | - | | | first assignment to `x` | help: make this binding mutable: `mut x` 3 | println!("x 的值是: {}", x); ...
warning: unused variable: `c` --> src/main.rs:20:9 | 20 |letc = CustomSmartPointer {data: String::from("my stuff")}; | ^help:ifthis is intentional, prefix it with an underscore: `_c` | = note: `#[warn(unused_variables)]` on by defaultwarning: unused variable: `d` ...
- lifetime: a variable's(变量) lifetime begins when it is created and ends when it is destroyed. - scope: the scope of the borrow is determined by where the reference is used. --- 在之前的例子中,我们看到,`thread::spawn`需要一个`'static`的闭包,但是为什么编译器会建议我们,将`&self`...
thread 'main' panicked at 'index out of bounds: the len is 5 but the index is 10', src/main.rs:19:19 note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace 程序在索引操作中使用一个无效的值时导致 运行时 错误。程序带着错误信息退出,并且没有执行最后的 println!
1fn main() {2let x: i32;3pritln!("{}", x);//use of possibly uninitialized variable 'x'4} Rust编译器会对代码做基本的静态分支流程分析,x在整个main函数中并没有绑定任何值,这样的代码会引起很多内存不安全的问题,比如计算结果非预期,程序崩溃,所以Rust编译器必须报错。
= "0.6.2", features = ["runtime-tokio-native-tls", "postgres"] }# middleware for axum router - https://github.com/tower-rs/tower-httptower-http = { version = "0.4.0", features = ["cors"] }# pre-req for using shuttle runtime tokio = "1.26.0"# get a time variable ...