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Concatenating strings

Concatenate strings with push_str and the + operator.

Concatenating Strings

Ways to append to a String:

let mut s = String::from("Merhaba");
s.push_str(", ");    // appends a &str
s.push('R');         // appends one char
s += "ust";          // appends a &str
println!("{s}");     // Merhaba, Rust

The + operator takes ownership of the String on the left: after let c = a + &b;, a can't be used, while b was only borrowed and stays usable.

Joining many pieces

When joining many pieces, chains of + become unreadable. format! takes ownership of none of its arguments and is the most readable option; for slices there are concat and join:

let ad = "Ada";
let soyad = "Lovelace";
let tam = format!("{ad} {soyad}");
let liste = ["a", "b", "c"].join(", ");   // "a, b, c"
let bitisik = ["x", "y"].concat();        // "xy"

Practice Build a greeting

Start with let mut s = String::from("Merhaba");. Call push_str(", "), push_str("Rust") and push('!'); then do let t = s + " 🦀"; and print t.

Starter code

main.rs
fn main() {
    // buraya yaz
}

Sample solution

main.rs
fn main() {
    let mut s = String::from("Merhaba");
    s.push_str(", ");
    s.push_str("Rust");
    s.push('!');
    let t = s + " 🦀";
    println!("{}", t);
}

Expected output

Merhaba, Rust! 🦀

Questions and answers

Review the lesson questions together with their answers. To test yourself, solve the lesson interactively.

1 Why doesn't <code>let a = String::from("x"); let b = String::from("y"); let c = a + b;</code> compile?

  • The right side must be a &str; write a + &b Correct answer
  • a is immutable
  • Strings can't be added
  • It compiles

Explanation: The + operation has the signature fn add(self, s: &str); that's why the second operand must be a reference.

2 Append one character

Question 
let mut s = String::from("ok");
s.____('!');
Answer 
let mut s = String::from("ok");
s.push('!');

Explanation: push appends a single char; push_str appends a &str.

3 Method and argument

Term Meaning
push_str &str
push char
a + &b Takes ownership of a
format! Takes no ownership

All lessons in Beginner

1 Rust basics

  1. What is Rust?
  2. Project with Cargo
  3. Your first program
  4. println! and formatting
  5. Comments
  6. Summary - Rust basics

2 Variables

  1. Variables with let
  2. Mutability with mut
  3. Constants with const
  4. Static variables
  5. Shadowing
  6. Summary - Variables

3 Data types

  1. Integers
  2. Floating point
  3. Bool and char
  4. Tuple
  5. Array
  6. Summary - Data types

4 Strings

  1. &str vs String
  2. Creating a String
  3. Concatenating strings
  4. format! macro
  5. String length
  6. Summary - Strings

5 Project: Calculator

  1. Project skeleton
  2. Reading input
  3. Computing
  4. Error handling
  5. Loop and exit

6 Functions

  1. Defining with fn
  2. Parameters
  3. Return value
  4. Expressions and statements
  5. Early return
  6. Summary - Functions

7 Control flow

  1. if-else
  2. match basics
  3. loop
  4. while loop
  5. for loop
  6. Summary - Control flow

8 Ownership

  1. What is ownership?
  2. Move semantics
  3. Copy trait
  4. Functions and ownership
  5. Return and ownership
  6. Summary - Ownership

9 Borrowing

  1. References
  2. Mutable reference
  3. Borrowing rules
  4. Dangling reference
  5. References and functions
  6. Summary - Borrowing

10 Slices

  1. String slices
  2. Slice syntax
  3. Array slices
  4. Slices and functions
  5. Range types
  6. Summary - Slices

11 Project: Guessing game

  1. Game skeleton
  2. Reading input
  3. Comparing numbers
  4. Random number
  5. Loop and exit

12 Structs

  1. Struct definition
  2. Creating an instance
  3. Tuple struct
  4. Unit-like struct
  5. Field update
  6. Summary - Structs

13 Methods

  1. impl block
  2. self parameter
  3. &mut self
  4. Associated functions
  5. Multiple impl blocks
  6. Summary - Methods

14 Enums

  1. Enum definition
  2. Variants
  3. Variants with data
  4. Option<T>
  5. Option instead of null
  6. Summary - Enums

15 Pattern matching

  1. match patterns
  2. Value binding
  3. if let
  4. while let
  5. _ wildcard
  6. Summary - Pattern matching

16 Project: To-do CLI

  1. Task model
  2. Adding
  3. Listing
  4. Marking done
  5. Reading commands

17 Vectors

  1. Vec<T>
  2. Push and pop
  3. Index and get
  4. Looping a vector
  5. with_capacity
  6. Summary - Vectors

18 Advanced strings

  1. String and &str conversion
  2. chars and bytes
  3. Slicing strings
  4. contains and replace
  5. split and join
  6. Summary - Advanced strings

19 Error handling

  1. Result<T, E>
  2. panic!
  3. ? operator
  4. match and Result
  5. unwrap and expect
  6. Summary - Error handling

20 Beginner final

  1. Vowel counter
  2. Average calculator
  3. Bank account
  4. Temperature converter