String in Rust

String in Rust might be more complex than you think. When people talk about string, it can have multiple meaning.

String literal

The simplest version of string is String literal

  let s = "hello";

If we hardcoded a string, then this is a literal String. It’s immutable by default, just like other data type.

String type `String`

It might be a bit confusing for now, but there is other string type we called String. Yeah.. same name.

The different with String literal, String type will be stored in Heap rather than stack since it’s mutable.

This is how to declare String type

let s = String::from("hello");

Using String::from()

Now s variable can be changed (mutated)

Convert literal string to String type

Using to_string we can do the following

let data = "initial contents";
let s = data.to_string();
// the method also works on a literal directly:
let s = "initial contents".to_string();
//same as
let s = String::from("initial contents");

Just remember that strings are UTF-8 encoded.

Updating a String

We can update a string, with push_str method

let mut s = String::from("foo");
s.push_str("bar");

Or to take a single character as a parameter

  let mut s = String::from("lo");
  s.push('l');

Concatenating String in Rust

We can also use a plus sign to concatenate a string in Rust

let s1 = String::from("Hello, ");
let s2 = String::from("world!");
let s3 = s1 + &s2;

If we used s1 plain like above, remember it can’t be used anymore. Instead use & if we still want to use the variable.

For more complex formatting we can use format macro.

let s1 = String::from("tic");
let s2 = String::from("tac");
let s3 = String::from("toe");

let s = format!("{}-{}-{}", s1, s2, s3);