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Creating an instance

Create a struct instance and access its fields.

Creating instances

When creating an instance, every field must be given a value; order doesn't matter. If the variable name equals the field name, the field init shorthand is used:

fn yeni_oyuncu(ad: String) -> Oyuncu {
    Oyuncu {
        ad,          // ad: ad
        puan: 0,
        aktif: true,
    }
}

A missing field is a "missing field" compile error; Rust doesn't assign default values automatically.

Printing with Debug

By default structs can't be printed with {} or {:?}. Once #[derive(Debug)] is added, {:?} gives one-line output and {:#?} indented output:

#[derive(Debug)]
struct Oyuncu { ad: String, puan: u32, aktif: bool }

let o = yeni_oyuncu(String::from("Ali"));
println!("{:?}", o);
// Oyuncu { ad: "Ali", puan: 0, aktif: true }

dbg!(&o) writes to stderr together with the file and line.

Practice Builder function

Define Oyuncu { ad: String, puan: u32, aktif: bool } with #[derive(Debug)]. Let fn yeni_oyuncu(ad: String) -> Oyuncu set puan: 0 and aktif: true using the field shorthand. Create one for "Ali" and print it with {:?}.

Starter code

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

Sample solution

main.rs
#[derive(Debug)]
struct Oyuncu {
    ad: String,
    puan: u32,
    aktif: bool,
}

fn yeni_oyuncu(ad: String) -> Oyuncu {
    Oyuncu {
        ad,
        puan: 0,
        aktif: true,
    }
}

fn main() {
    let o = yeni_oyuncu(String::from("Ali"));
    println!("{:?}", o);
}

Expected output

Oyuncu { ad: "Ali", puan: 0, aktif: true }

Questions and answers

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

1 Does <code>Oyuncu { ad, puan: 0 }</code> (without aktif) compile?

  • Yes, aktif stays undefined
  • It only warns
  • No: the field aktif is missing Correct answer
  • Yes, aktif becomes false

Explanation: All fields must be initialized. If you want defaults, use #[derive(Default)] and ..Default::default().

2 Derive Debug

Question 
#[derive(____)]
struct Oyuncu {
    ad: String,
}
Answer 
#[derive(Debug)]
struct Oyuncu {
    ad: String,
}

Explanation: derive(Debug) generates the {:?} format automatically.

3 Syntax and meaning

Term Meaning
Oyuncu { ad, .. } Field with shorthand
#[derive(Debug)] {:?} support
{:#?} Indented output
dbg!(&o) Writes to stderr

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