usestd::fs::File;usestd::io::{self,Read};fnread_username_from_file()->Result<String,io::Error>{letusername_file_result=File::open("hello.txt");letmutusername_file=matchusername_file_result{Ok(file)=>file,Err(e)=>returnErr(e),};letmutusername=String::new();matchusername_file.read_...
The first time we callexample_closurewith theStringvalue, the compiler infers the type ofxand the return type of the closure to beString. Those types are then locked into the closure inexample_closure, and we get a type error if we try to use a different type with the same closure. 不...
error[E0373]: closure may outlive the current function, but it borrows `name`, which is owned by the current function --> src\main.rs:3:29 | 3 | let hello_from_thread = || format!("Hello: {}", name); | ^^ --- `name` is borrowed here | | | may outlive borrowed value `...
运算符可被用于返回值类型为Result的函数,因为他被定义为与示例 9-6 中的match表达式有着完全相同的工作方式。match的return Err(e)部分要求返回值类型是Result,所以函数的返回值必须是Result才能与这个return相兼容。 让我们看看在main函数中使用?运算符会发生什么,如果你还记得的话其返回值类型是(): use std::f...
return &'a s; } } ``` That basically implies that we're going to find a str somewhere in the scope the reference to the u32 originated in, or somewhere _even earlier_. 即,需要一个`str`outlives`u32`,但这个`str`只能在函数体中产生,这是不可能的(因为即使产生,也会被自动 Drop 掉)。
let n = example_closure(5); ^ | expected struct `std::string::String`, found integer help: try using a conversion method: `5.to_string()` Closure至少实现了Fn, FnMut和FnOnce三种traits之中的一个。如果不需要创建Closure上下文中的变量,能传Closure的地方也能传Function 1 2 3 4 5 6 7 8 ...
fn my_function(x: u32, y: *mut u32) -> bool { // Function body. } 1. 2. 3. 在->标记后面的返回类型,当它是()("单元",空元组)时可以省略,它作为Rust的无效类型的等价物。函数的调用采用通常的foo(a, b, c)语法。
Closure至少实现了Fn, FnMut和FnOnce三种traits之中的一个。如果不需要创建Closure上下文中的变量,能传Closure的地方也能传Function impl<T>Cacher<T>whereT:Fn(u32)->u32,{fnnew(calculation:T)->Cacher<T>{Cacher{calculation,value:None,}}fnvalue(&mutself,arg:u32)->u32{matchself.value{Some(v)=>...
在Rust的源代码中,convert_nested_function_to_closure.rs文件位于路径rust/src/tools/rust-analyzer/crates/ide-assists/src/handlers/。该文件的作用是将嵌套函数转换为闭包。 嵌套函数是在另一个函数内部定义的函数。将嵌套函数转换为闭包可以使代码更加简洁和可读。闭包是一种可以捕获自己作用域的函数,可以在其他地...
[E0106]: missing lifetime specifier// --> src/main.rs:1:33// |// 1 | fn longest(x: &str, y: &str) -> &str {// | ^ expected lifetime parameter// |// = help: this function's return type contains a borrowed value, but the// signature does not say whether it is borrowed...