Rust Traits Quiz

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40 comprehensive questions on Rust's trait system, covering trait definitions, implementations, bounds, associated types, and trait objects — with 11 code examples demonstrating practical trait usage patterns.

40 Questions

~80 minutes

Question 1

What is a trait in Rust?

A way to define shared behavior that types can implement

A type of struct

A collection of functions

A way to define constants

Question 2

How do you define a trait in Rust?

trait TraitName { fn method(&self); }

struct TraitName { fn method(&self); }

class TraitName { fn method(&self); }

interface TraitName { fn method(&self); }

Question 3

How do you implement a trait for a type?

impl TraitName for TypeName { fn method(&self) { ... } }

trait TraitName for TypeName { fn method(&self) { ... } }

TypeName implements TraitName { fn method(&self) { ... } }

fn TraitName for TypeName { fn method(&self) { ... } }

Question 4

What will this trait implementation do?

rust

trait Drawable {
    fn draw(&self);
}

struct Circle;

impl Drawable for Circle {
    fn draw(&self) {
        println!("Drawing a circle");
    }
}

fn main() {
    let c = Circle;
    c.draw();
}

Prints 'Drawing a circle'

Compilation error

Prints nothing

Runtime error

Question 5

What are trait bounds in generic functions?

Constraints that specify what traits generic types must implement

Limits on the size of generic types

Bounds on trait method implementations

Memory bounds for trait objects

Question 6

How do you specify trait bounds in function signatures?

fn function<T: Trait>(param: T)

fn function<T>(param: T) where T: Trait

Both A and B are valid

fn function(param: Trait)

Question 7

What will this generic function with trait bounds do?

rust

trait Summary {
    fn summarize(&self) -> String;
}

fn notify<T: Summary>(item: &T) {
    println!("Breaking news! {}", item.summarize());
}

struct NewsArticle {
    headline: String,
}

impl Summary for NewsArticle {
    fn summarize(&self) -> String {
        format!("Headline: {}", self.headline)
    }
}

fn main() {
    let article = NewsArticle { headline: String::from("Rust is great!") };
    notify(&article);
}

Prints 'Breaking news! Headline: Rust is great!'

Compilation error

Prints 'Breaking news!'

Runtime error

Question 8

What are associated types in traits?

Types that are part of a trait definition but specified by implementations

Types that are automatically inferred

Types that are shared across all implementations

Types that cannot be changed

Question 9

How do you define an associated type in a trait?

trait TraitName { type AssociatedType; }

trait TraitName { associated type AssociatedType; }

trait TraitName<T> { ... }

trait TraitName { fn type AssociatedType; }

Question 10

How do you specify associated types in trait implementations?

impl TraitName for Type { type AssociatedType = ConcreteType; }

impl TraitName for Type<ConcreteType> { ... }

impl TraitName<ConcreteType> for Type { ... }

Associated types are automatically inferred

Question 11

What is the difference between generics and associated types?

Generics allow multiple implementations per type, associated types allow only one

Associated types are more flexible than generics

Generics are only for functions, associated types for traits

There is no functional difference

Question 12

What are trait objects?

References to types that implement a trait, enabling dynamic dispatch

Objects that contain trait definitions

Compiled trait implementations

Trait metadata

Question 13

How do you create a trait object?

&dyn Trait or Box<dyn Trait>

Trait::new()

dyn Trait {}

Trait {}

Question 14

What is the difference between static and dynamic dispatch?

Static dispatch is resolved at compile time, dynamic dispatch at runtime

Dynamic dispatch is faster

Static dispatch uses more memory

They are identical

Question 15

What will this trait object code do?

rust

trait Animal {
    fn make_sound(&self);
}

struct Dog;
struct Cat;

impl Animal for Dog {
    fn make_sound(&self) { println!("Woof!"); }
}

impl Animal for Cat {
    fn make_sound(&self) { println!("Meow!"); }
}

fn main() {
    let animals: Vec<Box<dyn Animal>> = vec![Box::new(Dog), Box::new(Cat)];
    for animal in animals {
        animal.make_sound();
    }
}

Prints 'Woof!' then 'Meow!'

Compilation error

Prints 'Woof!' twice

Runtime error

Question 16

What are default implementations in traits?

Method implementations provided in the trait definition that can be overridden

Automatic implementations generated by the compiler

Default parameter values for trait methods

Fallback implementations when custom ones fail

Question 17

How do you provide a default implementation in a trait?

trait Trait { fn method(&self) { /* default impl */ } }

trait Trait { default fn method(&self); }

trait Trait { fn method(&self) = default; }

Default implementations are not allowed

Question 18

Can you override default implementations?

Yes, by providing a custom implementation in the impl block

No, default implementations cannot be changed

Only partially

Only in certain contexts

Question 19

What are supertraits?

Traits that a trait depends on, requiring implementors to also implement the supertraits

Traits that inherit from other traits

Parent traits in a hierarchy

Traits with higher priority

Question 20

How do you specify supertraits?

trait SubTrait: SuperTrait { ... }

trait SubTrait extends SuperTrait { ... }

trait SubTrait implements SuperTrait { ... }

Supertraits are automatically inferred

Question 21

What are orphan rules in trait implementations?

Rules that prevent implementing external traits for external types

Rules about trait inheritance

Rules about trait object creation

Rules about default implementations

Question 22

When can you implement a trait for a type?

When either the trait or the type is defined in your crate

Always, for any trait and type

Only for traits and types in the standard library

Only when both are defined locally

Question 23

What are marker traits?

Traits with no methods that convey semantic meaning to the compiler

Traits that mark code locations

Traits used for debugging

Traits that implement automatically

Question 24

What is the Copy trait?

A marker trait that indicates types can be copied by simply copying bits

A trait for copying files

A trait for copying strings

A trait that implements clone automatically

Question 25

What is the difference between Copy and Clone?

Copy is implicit and cheap, Clone is explicit and may be expensive

Clone is implicit, Copy is explicit

Copy works for all types, Clone for some

There is no difference

Question 26

How do you derive common traits automatically?

#[derive(Debug, Clone, Copy)] above struct/enum definitions

impl Debug for Struct automatically

use derive::Debug;

Automatic derivation is not possible

Question 27

What traits can typically be derived?

Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord, Hash

All traits can be derived

Only Debug and Display

Only standard library traits

Question 28

What is trait coherence (also called orphan rules)?

Rules ensuring that trait implementations are unique and predictable

Rules about trait compilation order

Rules about trait performance

Rules about trait naming

Question 29

What are blanket implementations?

Trait implementations that apply to all types meeting certain bounds

Implementations that cover multiple traits

Implementations that are automatically generated

Implementations for built-in types

Question 30

What will this blanket implementation do?

rust

trait Display {
    fn display(&self) -> String;
}

impl<T: std::fmt::Display> Display for T {
    fn display(&self) -> String {
        format!("{}", self)
    }
}

fn main() {
    let num = 42;
    println!("{}", num.display());
}

Prints '42' using the blanket implementation

Compilation error

Prints nothing

Runtime error

Question 31

What are associated constants in traits?

Constants that are part of a trait definition

Constants that are automatically calculated

Constants shared across all implementations

Constants that cannot be overridden

Question 32

How do you define an associated constant?

trait Trait { const CONSTANT: Type = value; }

trait Trait { constant CONSTANT: Type; }

trait Trait { static CONSTANT: Type; }

Associated constants cannot be defined

Question 33

What is the Sized trait?

A marker trait indicating types with known size at compile time

A trait for resizing collections

A trait for sized types only

A trait that makes types larger

Question 34

What does ?Sized mean in trait bounds?

Allows both sized and unsized types (like slices)

Makes types unsized

Requires sized types only

Optimizes for sized types

Question 35

What are object safety rules for traits?

Rules that determine if a trait can be used as a trait object

Rules about trait object performance

Rules about trait compilation

Rules about trait naming

Question 36

What makes a trait object-safe?

No associated types, all methods have Self: Sized or use &self/&mut self

Having default implementations

Being implemented by many types

Using generics

Question 37

What is the Drop trait used for?

Custom cleanup logic when values go out of scope

Dropping trait objects

Dropping references

Automatic memory deallocation

Question 38

How do you implement the Drop trait?

impl Drop for Type { fn drop(&mut self) { ... } }

impl Drop for Type { fn cleanup(&mut self) { ... } }

Drop implementations are automatic

Use the drop keyword

Question 39

What is the Deref trait used for?

Smart pointer dereferencing with the * operator

Dereferencing raw pointers

Dereferencing references

Automatic dereferencing

Question 40

In a scenario where you're designing a drawing API that needs to work with different shapes that can be rendered to different backends, how would you structure the trait hierarchy?

Create a Drawable trait with associated types for different backends, and implement it for each shape type

Use inheritance with base Shape class

Use enums for different shape types

Use functions for each shape and backend combination

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Rust Traits Quiz

Question 1

Question 2

Question 3

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15

Question 16

Question 17

Question 18

Question 19

Question 20

Question 21

Question 22

Question 23

Question 24

Question 25

Question 26

Question 27

Question 28

Question 29

Question 30

Question 31

Question 32

Question 33

Question 34

Question 35

Question 36

Question 37

Question 38

Question 39

Question 40

About This Traits Quiz

What You Will Practise

Other Quiz Categories

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Variables and Mutability

Data Types

Control Flow

Functions

Ownership

Borrowing

Lifetimes

Strings

Collections

Slices

Pattern Matching

Enums

Struct

Modules

Traits

Generic

Iterators

Closures

Error Handling

File and I/O Operations

Smart Pointers

Concurrency

Async Programming

Memory Management

Macros

Attributes

Testing

Crate Architecture

Performance and Optimization