有办法修复此代码还是我应该要求更改数据结构？

Question

我对此失去了理智（因为我不是一个非常有逻辑的人）。

RUST 游乐场

我无法更改数据部分。

从下面的代码返回的字符串是

A = 1 AND (B = 2 OR C = 3 OR D = 4 OR )

而不是我需要的（

A = 1 AND (B = 2 OR C = 3 OR D = 4)

）。

我不明白的是如何避免最后一个“OR”。

如何修复以下代码？

enum Token {
    Str(&'static str),
    Value(&'static str),
    StartGroup(&'static str),
    EndGroup,
}

fn main() {
    let data: Vec<Vec<Token>> = vec![
        vec![Token::Str("A = "), Token::Value("1")],
        vec![Token::Str(" AND ("), Token::StartGroup(" OR ")],
        vec![Token::Str("B = "), Token::Value("2")],
        vec![Token::Str("C = "), Token::Value("3")],
        vec![Token::Str("D = "), Token::Value("4")],
        vec![Token::EndGroup, Token::Str(")")],
    ];

    let result = construct_string(data);

    assert_eq!("A = 1 AND (B = 2 OR C = 3 OR D = 4)", result);
}

fn construct_string(tokens: Vec<Vec<Token>>) -> String {
    let mut result = String::new();

    let mut current = String::new();
    let mut next = String::new();

    for token in tokens {
        for part in token {
            match part {
                Token::Str(str) => {
                    result.push_str(str);
                }
                Token::Value(val) => {
                    result.push_str(val);
                }
                Token::StartGroup(group) => {
                    next = group.to_string();
                }
                Token::EndGroup => {
                    current = String::new();
                    next = String::new();
                }
            }
        }

        if !current.is_empty() {
            result.push_str(&current);
        }

        current = next.to_string();
    }

    result
}

Answer 1

我将

EndGroup

移至之前的向量，它起作用了：

enum Token {
    Str(&'static str),
    Value(&'static str),
    StartGroup(&'static str),
    EndGroup,
}

fn main() {
    let data: Vec<Vec<Token>> = vec![
        vec![Token::Str("A = "), Token::Value("1")],
        vec![Token::Str(" AND ("), Token::StartGroup(" OR ")],
        vec![Token::Str("B = "), Token::Value("2")],
        vec![Token::Str("C = "), Token::Value("3")],
        vec![Token::Str("D = "), Token::Value("4"), Token::EndGroup],
        vec![ Token::Str(")")],
    ];

    let result = construct_string(data);

    assert_eq!("A = 1 AND (B = 2 OR C = 3 OR D = 4)", result);
}

fn construct_string(tokens: Vec<Vec<Token>>) -> String {
    let mut result = String::new();

    let mut current = String::new();
    let mut next = String::new();

    for token in tokens {
        for part in token {
            match part {
                Token::Str(str) => {
                    result.push_str(str);
                }
                Token::Value(val) => {
                    result.push_str(val);
                }
                Token::StartGroup(group) => {
                    next = group.to_string();
                }
                Token::EndGroup => {
                    current = String::new();
                    next = String::new();
                }
            }
        }

        if !current.is_empty() {
            result.push_str(&current);
        }

        current = next.to_string();
    }

    result
}

编辑

在

construct_string

中应用了修复，请看一下（想法是区分分隔符是否必须出现）：

enum Token {
    Str(&'static str),
    Value(&'static str),
    StartGroup(&'static str),
    EndGroup,
}

fn main() {
    let data: Vec<Vec<Token>> = vec![
        vec![Token::Str("A = "), Token::Value("1")],
        vec![Token::Str(" AND ("), Token::StartGroup(" OR ")],
        vec![Token::Str("B = "), Token::Value("2")],
        vec![Token::Str("C = "), Token::Value("3")],
        vec![Token::Str("D = "), Token::Value("4")],
        vec![Token::EndGroup, Token::Str(")")],
    ];

    let result = construct_string(data);

    assert_eq!("A = 1 AND (B = 2 OR C = 3 OR D = 4)", result);
}

fn construct_string(tokens: Vec<Vec<Token>>) -> String {
    let mut result = String::new();

    //let mut current = String::new();
    let mut next = String::new();
    
    let mut new_group = true;

    for token in tokens {
        for part in token {
            match part {
                Token::Str(str) => {
                    if !new_group {
                        result.push_str(&next);
                    }
                    new_group = false;
                    result.push_str(str);
                }
                Token::Value(val) => {
                    result.push_str(val);
                }
                Token::StartGroup(group) => {
                    new_group = true;
                    next = group.to_string();
                }
                Token::EndGroup => {
                    //current = String::new();
                    next = String::new();
                }
            }
        }

        //if !current.is_empty() {
          //  result.push_str(&current);
        //}

        //current = next.to_string();
    }

    result
}