Exploring Strings in Rust

• 计算机是如何存储字符串的？

  • 以字节为单位，根据特定规则（如 ASCII，Unicode）来建立字节与字符之间的映射
  • ASCII：1 个字符=1 个字节
  • Unicode：1 个字符=1~4 个字节

• 在 Rust 中，字符串使用 UTF-8 编码

• &str vs str

  • Both called string slice
  • Primitive Type str
    • let string: str = "banana"; cannot compile.
    • str 动态大小，编译器不知道它的大小
    • An strdefines a slice of a block of data in memory which are meant to be interpreted as a sequence of characters and that’s all. It is uncertain where it is stored and how long that slice would be. This is why we can not use this type in a plain way in the time of writing.
  • &str: shared reference to str
    • let string: &'static str = "banana";
    • the size of a reference is always known at compile time.
    • shared reference & always points to valid data and that data stays immutable under it.
    • &mut str mutable reference can be used if the pointer points to the heap.
    • However: Even in a few cases we can take a mutable reference to it and might change the contents of the underlying data, it can not grow or shrink in size

• String : vector of characters

  • can grow or shrink in size

  let mut banana_string: String = String::from("banana");
  let mut cherry_string: String = String::from("I want a cherry");
  banana_string += " ";
  cherry_string += &banana_string;
  

• &String : pointer to String

• Box<&str> allocate on heap and take a pointer

  • let string: Box<&str> = Box::new(“banana”);

• C/C++ 使用 null-terminated \\0 字符串

• Rust 使用 fat pointers or heap-allocated structs

deref coercions

https://rustwiki.org/zh-CN/book/ch15-02-deref.html#函数和方法的隐式解引用强制转换

String → &str

fn hello(name: &str) {
    println!("Hello, {}!", name);
}

fn main() {
    let m = Box::new(String::from("Rust")); // type: Box<String>
    hello(&m); // &Box<String> -> &String -> &str
}