为什么在推送到字符串时，已转换为char的字节似乎没有正确的类型？

Question

使用this回答我正在尝试编写一个Rust函数，它将128位整数转换为基数为62的数字。

fn encode_as_chars(mut integer: u128) {
    let alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".as_bytes();
    let base: u128 = 62;
    let mut encoded: String;

    while integer != 0 {
        encoded = encoded.push(alphabet[(integer % base) as usize] as char);
        integer /= base;
    }
    encoded;
}

我使用as_bytes()通过索引访问字母表中的字符并将字节强制转换为char，打算使用String::push将char推送到编码的字符串。但是编译器抱怨这个，返回错误

error[E0308]: mismatched types
 --> src/lib.rs:7:19
  |
7 |         encoded = encoded.push(alphabet[(integer % base) as usize] as char);
  |                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ expected struct `std::string::String`, found ()
  |
  = note: expected type `std::string::String`
             found type `()`

我尝试使用to_owned()显式地为char分配内存：

let character: char = (alphabet[(integer % base) as usize] as char).to_owned();
encoded = encoded.push( character );

但是这返回了同样的错误。

为什么在推送到字符串时，已转换为char的字节似乎没有正确的类型？

Answer 1

这是因为字符串类型的push不返回任何内容而ergo返回()

将您的代码更改为：

// `->` specifies return type
fn encode_as_chars( mut integer: u128 ) -> String {
    let alphabet = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ".as_bytes();
    let base: u128 = 62;
    let mut encoded: String = "".to_string(); // you need to initialize every variable in Rust

    while integer != 0 {
        encoded.push( alphabet[(integer % base) as usize] as char );
        integer /= base;
    }

    encoded // return encoded
}