Rust Programming: String

A string in Rust is a sequence of Unicode characters encoded in UTF-8. Rust has two main string types: String and &str.

• String is a growable, mutable, owned, UTF-8 encoded string type. It is stored on the heap and can be modified and reallocated in memory as needed.
• &str is a string slice that refers to a specific sequence of characters in a string. It is an immutable reference, meaning it cannot be changed once bound to a particular string. String slices can be created from String objects, string literals, and other string slices.

The most common way to create a String object is to use the String::new() function. This will create a new empty String object. You can then add characters to the String object using the push_str() method.

Rust

use std::string::String;

fn main() {
    let mut my_string = String::new();

    my_string.push_str("Hello, world!");

    println!("{}", my_string);
}

Output:

Hello, world!

You can also create a String object from a string literal using the following syntax:

Rust

let my_string = "Hello, world!".to_string();

String slices can be created using the &[] syntax. For example, the following code creates a string slice from the string literal "Hello, world!".

Rust

let my_string_slice = &"Hello, world!";

String slices can also be created from String objects using the as_str() method. For example, the following code creates a string slice from the String object my_string.

Rust

let my_string_slice = my_string.as_str();

String slices are often used as function arguments and return values. This is because they are immutable and cannot be modified by the function. This makes them safer and more efficient to pass around in code.

When to use String vs &str

In general, you should use String if you need to create a mutable string that you can modify and reallocate in memory. You should use &str if you need a view of a string that you do not need to modify.

Here are some specific examples:

• Use String if you need to read a string from a file or network connection.
• Use String if you need to build a string dynamically at runtime.
• Use String if you need to pass a mutable string to a function.
• Use &str if you need to pass a string to a function that does not need to modify it.
• Use &str if you need to return a string from a function that does not own it.