错误 [E0308]：不匹配的类型需要 `()`，找到了 `bool`。如何消除这个错误？

Question

检查回文的程序

pub fn is_palindrome(str: &str, start: i32, end: i32) -> bool

{

    //if empty string
    if str.is_empty() {
        true
    }

    // If there is only one character
    if start == end {
        true
    }

    // If first and last
    // characters do not match
    if str.chars().nth(start as usize) != str.chars().nth(end as usize) {
        false
    }

    // If there are more than
    // two characters, check if
    // middle substring is also
    // palindrome or not.
    if start < end + 1 {
        is_palindrome(str, start + 1, end - 1)
    }
    true
}

这是我的代码，我在 return 语句中出错。它说错误[E0308]：类型不匹配预期 ()，发现 bool 请告诉如何解决这个问题。

Answer 1

你忘了return statements which has to be used if you want to return a value earlier from within a function (See also Functions):

pub fn is_palindrome(str: &str, start: i32, end: i32) -> bool {

    //if empty string
    if str.is_empty() {
        return true;
    }

    // If there is only one character
    if start == end {
        return true;
    }

    // If first and last
    // characters do not match
    if str.chars().nth(start as usize) != str.chars().nth(end as usize) {
        return false;
    }

    // If there are more than
    // two characters, check if
    // middle substring is also
    // palindrome or not.
    if start < end + 1 {
        return is_palindrome(str, start + 1, end - 1);
    }
    true
}

错误 [E0308]：不匹配的类型需要 `()`，找到了 `bool`。如何消除这个错误？

error[E0308]: mismatched types expected `()`, found `bool`. How to remove this error?

types

rust

return

boolean

palindrome