测验3: exercises/quiz3.rs

题目

rust

// quiz3.rs
//
// This quiz tests:
// - Generics
// - Traits
//
// An imaginary magical school has a new report card generation system written
// in Rust! Currently the system only supports creating report cards where the
// student's grade is represented numerically (e.g. 1.0 -> 5.5). However, the
// school also issues alphabetical grades (A+ -> F-) and needs to be able to
// print both types of report card!
//
// Make the necessary code changes in the struct ReportCard and the impl block
// to support alphabetical report cards. Change the Grade in the second test to
// "A+" to show that your changes allow alphabetical grades.
//
// Execute `rustlings hint quiz3` or use the `hint` watch subcommand for a hint.

// I AM NOT DONE

pub struct ReportCard {
    pub grade: f32,
    pub student_name: String,
    pub student_age: u8,
}

impl ReportCard {
    pub fn print(&self) -> String {
        format!("{} ({}) - achieved a grade of {}",
            &self.student_name, &self.student_age, &self.grade)
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn generate_numeric_report_card() {
        let report_card = ReportCard {
            grade: 2.1,
            student_name: "Tom Wriggle".to_string(),
            student_age: 12,
        };
        assert_eq!(
            report_card.print(),
            "Tom Wriggle (12) - achieved a grade of 2.1"
        );
    }

    #[test]
    fn generate_alphabetic_report_card() {
        // TODO: Make sure to change the grade here after you finish the exercise.
        let report_card = ReportCard {
            grade: 2.1,
            student_name: "Gary Plotter".to_string(),
            student_age: 11,
        };
        assert_eq!(
            report_card.print(),
            "Gary Plotter (11) - achieved a grade of A+"
        );
    }
}

本次测验涉及的内容：

泛型
Trait

一个虚构的魔法学校，有一个用Rust编写的新成绩单生成系统！目前系统只支持创建以数字表示学生成绩的成绩单（比如1.0 -> 5.5）。然而，学校也按照字母顺序颁发成绩(A+ -> F-)，并且需要能够打印两种类型的成绩单。

在ReportCard结构体和impl块中进行必要的代码修改，以支持字母顺序的成绩单。将第二次测试中的成绩更改为A+，以表明您的更改已生效。

题目解析

我们先修改ReportCard结构体，让它先支持泛型，以便能够同时支持浮点数和字符串。

rust

pub struct ReportCard { 
    pub grade: f32, 
pub struct ReportCard<T> { 
    pub grade: T, 
    pub student_name: String,
    pub student_age: u8,
}

接着，我们还要看impl块，在print方法中，我们使用了{}输出，这就要求grade这个泛型参数需要首先实现了std::fmt::Display Trait。

rust

impl ReportCard { 
impl<T: std::fmt::Display> ReportCard<T> { 
    pub fn print(&self) -> String {
        format!(
            "{} ({}) - achieved a grade of {}",
            &self.student_name, &self.student_age, &self.grade
        )
    }
}

最后我们还需要把单元测试里面的第二个成绩修改为A+：

rust

#[test]
    fn generate_alphabetic_report_card() {
        // TODO: Make sure to change the grade here after you finish the exercise.
        let report_card = ReportCard {
            grade: 2.1,  
            grade: "A+",  
            student_name: "Gary Plotter".to_string(),
            student_age: 11,
        };
        assert_eq!(
            report_card.print(),
            "Gary Plotter (11) - achieved a grade of A+"
        );
    }

测验3: exercises/quiz3.rs ​

题目 ​

题目解析 ​

参考资料 ​

测验3: exercises/quiz3.rs

题目

题目解析

参考资料