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Summary - Pattern matching

Combine match, if let and the _ wildcard to build a command interpreter.

Pattern matching summary

match is exhaustive and runs the first arm that fits. Patterns: literals, |, ..= ranges, tuple/struct/enum destructuring, @ binding, _ and ... Use if let for a single pattern, while let for loops, let-else for early exit and matches! for a bool. Arms can also have a guard: x if x < 0 => ...

Match guards

For conditions that a pattern alone can't express, an if is added to the arm:

fn sinif(n: i32) -> &'static str {
    match n {
        x if x < 0 => "negatif",
        0 => "sıfır",
        x if x % 2 == 0 => "çift",
        _ => "tek",
    }
}

A guard applies to all patterns joined with |: 1 | 2 if kosul → (1 or 2) and the condition.

Practice Number class

Write the function fn sinif(n: i32) -> &'static str above with match guards. Print the results for -3, 0, 4 and 7 on one line separated by spaces.

Starter code

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

Sample solution

main.rs
fn sinif(n: i32) -> &'static str {
    match n {
        x if x < 0 => "negatif",
        0 => "sıfır",
        x if x % 2 == 0 => "çift",
        _ => "tek",
    }
}

fn main() {
    println!("{} {} {} {}", sinif(-3), sinif(0), sinif(4), sinif(7));
}

Expected output

negatif sıfır çift tek

Questions and answers

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

1 What is needed for exhaustiveness when using guarded arms?

  • Usually an unguarded final arm (like _) Correct answer
  • Nothing; the compiler solves the conditions
  • A guard on every arm
  • An else block

Explanation: The compiler doesn't evaluate guard expressions, so an unguarded arm must cover the remaining cases.

2 Add a guard

Question 
match n {
    x ____ x < 0 => "negatif",
    _ => "pozitif ya da sıfır",
}
Answer 
match n {
    x if x < 0 => "negatif",
    _ => "pozitif ya da sıfır",
}

Explanation: A match guard is written with if after the pattern.

3 sinif() input and result

Term Meaning
-3 negatif
0 sıfır
4 çift
7 tek

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