相关疑难解决方法(0)

常规浮点文字不起作用：

extern crate num_traits;

use num_traits::float::Float;

fn scale_float<T: Float>(x: T) -> T {
    x * 0.54
}

fn main() {
    let a: f64 = scale_float(1.23);
}

extern crate num_traits;

use num_traits::float::Float;

fn scale_float<T: Float>(x: T) -> T {
    x * 0.54
}

fn main() {
    let a: f64 = scale_float(1.23);
}

我编写了一个通用函数来检查给定数字是否为偶数：

use std::ops::Rem;

fn main() {
    let x: u16 = 31;
    let y: u32 = 40;

    println!("x = {}, y = {}", is_even(x), is_even(y));
}

fn is_even<T: Rem<Output = T> + PartialEq>(n: T) -> bool {
    n % 2 == 0
}

它会产生编译器错误：

use std::ops::Rem;

fn main() {
    let x: u16 = 31;
    let y: u32 = 40;

    println!("x = {}, y = {}", is_even(x), is_even(y));
}

fn is_even<T: Rem<Output = T> + PartialEq>(n: T) -> bool {
    n % …

下面是一个通用类型Foo。如何正确实现该addOne方法：

struct Foo<T> {
    n: T,
}

impl<T> Foo<T> {
    fn addOne(self) -> T {
        self.n + 1
    }
}

fn main() {
    let a = Foo { n: 5 };
    println!("{}", a.addOne());
}

我期望输出为6，但是此代码无法编译：

struct Foo<T> {
    n: T,
}

impl<T> Foo<T> {
    fn addOne(self) -> T {
        self.n + 1
    }
}

fn main() {
    let a = Foo { n: 5 };
    println!("{}", a.addOne());
}

我越来越熟悉 Rust 泛型，但我不知道出了什么问题。

use std::collections::BTreeMap;

fn frequency<T: Ord + Clone>(vec: &Vec<T>) -> BTreeMap<T, u32> {
    let mut movie_reviews = BTreeMap::new();
    let mut vec_ = Vec::new();
    vec.push(1);
    movie_reviews
}

我不知道为什么它需要 type T：

use std::collections::BTreeMap;

fn frequency<T: Ord + Clone>(vec: &Vec<T>) -> BTreeMap<T, u32> {
    let mut movie_reviews = BTreeMap::new();
    let mut vec_ = Vec::new();
    vec.push(1);
    movie_reviews
}

我有以下代码片段：

use num_bigint::*; // 0.2.2
use num_traits::*; // 0.2.8
use std::ops::*;

fn xgcd(b: &BigInt, a: &BigInt) -> (BigInt, BigInt, BigInt) {
    let mut x0: BigInt = One::one();
    let mut x1: BigInt = Zero::zero();
    let mut y0: BigInt = Zero::zero();
    let mut y1: BigInt = One::one();
    let mut q = 0;
    while a != Zero::zero() {
        q = b.div(a);
        b = a;
        a = &b.rem(a);
        x0 = x1;
        x1 = x0 - q * x1;
        y0 = y1;
        y1 = y0 …