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Multiple impl blocks

Write multiple impl blocks for a single struct.

Multiple impl blocks

A type can have several impl blocks; the compiler combines them all. This is used to group constructors, calculations and helpers separately:

impl Kutu {
    fn new(en: u32, boy: u32) -> Self { Self { en, boy } }
}

impl Kutu {
    fn alan(&self) -> u32 { self.en * self.boy }
    fn kenar_toplami(&self) -> u32 { 2 * (self.en + self.boy) }
}

Separate blocks become especially meaningful for trait implementations (impl Display for Kutu) and conditional generic implementations.

Calling methods inside methods

A method can call other methods of the same type with self.; this also holds for methods in different blocks:

impl Kutu {
    fn kare_mi(&self) -> bool {
        self.en == self.boy
    }
    fn tanim(&self) -> String {
        let tur = if self.kare_mi() { "kare" } else { "dikdörtgen" };
        format!("{tur}, alan {}", self.alan())
    }
}

Practice Two blocks

Write new in a first impl Kutu block, and the methods alan and kenar_toplami (2 × (en + boy)) in a second block. Print both results for Kutu::new(3, 4) separated by a space.

Starter code

main.rs
struct Kutu {
    en: u32,
    boy: u32,
}

fn main() {
    // buraya yaz
}

Sample solution

main.rs
struct Kutu {
    en: u32,
    boy: u32,
}

impl Kutu {
    fn new(en: u32, boy: u32) -> Self {
        Self { en, boy }
    }
}

impl Kutu {
    fn alan(&self) -> u32 {
        self.en * self.boy
    }
    fn kenar_toplami(&self) -> u32 {
        2 * (self.en + self.boy)
    }
}

fn main() {
    let k = Kutu::new(3, 4);
    println!("{} {}", k.alan(), k.kenar_toplami());
}

Expected output

12 14

Questions and answers

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

1 What happens if two separate <code>impl Kutu</code> blocks have a method with the same name <code>alan</code>?

  • Compile error: duplicate definition Correct answer
  • The later one overrides the earlier
  • Both are called
  • It becomes an overload

Explanation: Rust has no function overloading; two associated items with the same name for the same type is error E0592.

2 Call another method

Question 
fn tanim(&self) -> String {
    format!("alan {}", ____.alan())
}
Answer 
fn tanim(&self) -> String {
    format!("alan {}", self.alan())
}

Explanation: Another method of the same instance is called through self.

3 Case and result

Term Meaning
Two impl Kutu blocks Combined
Two methods with the same name E0592
self.alan() Inner call
impl Display for Kutu Trait implementation

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