rust

问题 How can I attempt something like the following in Rust? The builder class is a trait object which returns another trait object (type erasure) where the implementation that is selected is defined by the specific object of the builder trait that we are using. trait Builder { // I want this trait to return a trait object fn commits(&self) -> dyn Commit; fn finish(&self); } trait Commit { } struct FooBuilder { } struct FooCommit { } impl Builder for FooBuilder { fn commits(&self) -> impl Commit {

问题 How can I attempt something like the following in Rust? The builder class is a trait object which returns another trait object (type erasure) where the implementation that is selected is defined by the specific object of the builder trait that we are using. trait Builder { // I want this trait to return a trait object fn commits(&self) -> dyn Commit; fn finish(&self); } trait Commit { } struct FooBuilder { } struct FooCommit { } impl Builder for FooBuilder { fn commits(&self) -> impl Commit {

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I need to calculate 21 factorial in my project. fn factorial(num: u64) -> u64 { match num { 0 => 1, 1 => 1, _ => factorial(num - 1) * num, } } fn main() { let x = factorial(21); println!("The value of 21 factorial is {} ", x); } When running this code, I get an error: thread 'main' panicked at 'attempt to multiply with overflow', src\main.rs:5:18 回答1: A u64 can’t hold 21! (it’s between 2^65 and 2^66), but a u128 can. 回答2: I need to calculate 21 factorial in my project. 21! doesn't fit in a 64

问题 I am trying to implement Debug for my custom List<T> using a while loop. use std::cell::RefCell; use std::rc::Rc; type Link<T> = Option<Rc<RefCell<Node<T>>>>; struct Node<T> { val: T, next: Link<T>, } struct List<T> { head: Link<T>, tail: Link<T>, len: usize, } use std::fmt; impl<T: fmt::Debug> fmt::Debug for List<T> { fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result { let mut temp = &self.head; while let Some(r) = temp { write!(f, "{:?} -> ", r.borrow().val); temp = &r.borrow().next;

问题 This question already has answers here : How to mock external dependencies in tests? [duplicate] (1 answer) How to mock specific methods but not all of them in Rust? (2 answers) How can I test stdin and stdout? (1 answer) Is there a way of detecting whether code is being called from tests in Rust? (1 answer) What is the proper way to use the `cfg!` macro to choose between multiple implementations? (1 answer) Closed 8 days ago . I'm trying to run unit tests on a function reducer . reducer