Rust - LinkedIn Skill Assessments Quizzes with Answers

Rust (Programming Language)

Q1. Which type cast preserves the mathematical value in all cases?

  • i64 as i32
  • usize as u64
  • i32 as i64
  • f64 as f32

Q2. What do the vertical bars represent here?

str:🧵:spawn(|| {
    println!("LinkedIn");
});
  • a closure
  • a thread
  • a future
  • a block

reference

Q3. Which choice is not a scalar data type?

  • integer
  • float
  • boolean
  • tuple

Q4. _ cannot be destructured.

  • Traits
  • Tuples
  • Enums
  • Structs

reference

Q5. Which cargo command checks a program for error without creating a binary executable?

  • cargo –version
  • cargo init
  • cargo build
  • cargo check
  • It’s creating a pointer on the heap that points to a value on the stack.
  • It’s creating a pointer on the stack that points to a value on the heap.
  • It’s creating a memory guard around values to prevent illegal access.
  • It’s an abstraction that refers to ownership. “Boxed” values are clearly labelled.

Q7. What is an alternative way of writing slice that produces the same result?

...
let s = String::form("hello");
let slice = &s[0..2];
  • let slice = &s[len + 2];
  • let slice = &s[len - 2];
  • let slice = &s.copy(0..2);
  • let slice = &s[..2];

Q8. Using the ? operator at the end of an expression is equivalent to _.

  • a match pattern that branches into True or False
  • calling ok_error()
  • calling panic!()
  • a match pattern that may result an early return

Q9. Which is valid syntax for defining an array of i32 values?

  • Array::with_capacity(10)
  • [i32]
  • Array::new(10)
  • [i32; 10]

Q10. What syntax is required to take a mutable reference to T, when used within a function argument?

fn increment(i: T) {
    // body elided
}
  • *mut T
  • mut ref T
  • mut &T
  • &mut T

Q11. The smart pointers Rc and Arc provide reference counting. What is the API for incrementing a reference count?

  • .add()
  • .incr()
  • .clone()
  • .increment()

reference

Q12. What happens when an error occurs that is being handled by the question mark (?) operator?

  • The error is reported and execution continues.
  • An exception is raised. The effect(s) of the exception are defined by the error! macro.
  • The program panics immediately.
  • Rust attempts to convert the error to the local function’s error type and return it as Result::Err. If that fails, the program panics.
  • /*
  • #
  • //!
  • //

Q14. In matching patterns, values are ignored with _.

  • .ignore()
  • an underscore (_)
  • ..
  • skip

Q15. Defining a _ requires a lifetime parameter.

  • function that ends the lifetime of one of its arguments
  • struct that contains a reference to a value
  • function with a generic argument
  • struct that contains a reference to a boxed value

Rust book reference

Q16. Which example correctly uses std::collections::HashMap’s Entry API to populate counts?

use std::collections::HashMap;
fn main() {
    let mut counts = HashMap::new();
    let text = "LinkedIn Learning";
    for c in text.chars() {
        // Complete this block
    }
    println!("{:?}", counts);
}
for c in text.chars() {
    if let Some(count) = &mut counts.get(&c) {
        counts.insert(c, *count + 1);
    } else {
        counts.insert(c, 1);
    };
}
for c in text.chars() {
    let count = counts.entry(c).or_insert(0);
    *count += 1;
}
for c in text.chars() {
    let count = counts.entry(c);
    *count += 1;
}
for c in text.chars() {
    counts.entry(c).or_insert(0).map(|x| x + 1);
}

reference

Q17. Which fragment does not incur memory allocations while writing to a “file” (represented by a Vec)?

use std::collections::HashMap;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    let mut v = Vec::<u8>::new();

    let a = "LinkedIn";
    let b = 123;
    let c = '🧀';

    // replace this line

    println!("{:?}", v);

    Ok(())
}
write!(&mut v, "{}{}{}", a, b, c)?;
v.write(a)?;
v.write(b)?;
v.write(c)?;
v.write(a, b, c)?;
v.write_all(a.as_bytes())?;
v.write_all(&b.to_string().as_bytes())?;
c.encode_utf8(&mut v);
  1. Answered in rust user forum
  2. reference

Q18. Does the main function compile? If so, why? If not, what do you need to change?

fn main() {
    let Some(x) = some_option_value;
}
  • The code does not compile. let statements require a refutable pattern. Add if before let.
  • The code compiles. let statements sometimes require a refutable pattern.
  • The code does not compile. let statements requires an irrefutable pattern. Add if before let.
  • The code compiles. let do not require a refutable pattern.

Q19. Which statement about lifetimes is false?

  • Lifetimes were redundantly specified in previous version of Rust.
  • Lifetimes are specified when a struct is holding a reference to a value.
  • Lifetimes are specified when certain values must outlive others.
  • Lifetimes are always inferred by the compiler.

Q20. When used as a return type, which Rust type plays a similar role to Python’s None, JavaScript’s null, or the void type in C/C++?

  • !
  • None
  • Null
  • ()

Q21. To convert a Result to an Option, which method should you use?

  • .as_option()
  • .ok()
  • .to_option()
  • .into()

Q22. Which statement about the Clone and Copy traits is false?

  • Copy is enabled for primitive, built-in types.
  • Without Copy, Rust applies move semantics to a type’s access.
  • When using Clone, copying data is explicit.
  • Until a type implements either Copy or Clone, its internal data cannot be copied.

ref from stack overflow

Q23. Why does this code not compile?

fn returns_closure() -> dyn Fn(i32) -> i32 {
    |x| x + 1
}
  • The returned fn pointer and value need to be represented by another trait.
  • Closures are types, so they cannot be returned directly from a function.
  • Closures are types and can be returned only if the concrete trait is implemented.
  • Closures are represented by traits, so they cannot be a return type.

Rust book reference

Q24. What smart pointer is used to allow multiple ownership of a value in various threads?

  • Arc<T>
  • Box<T>
  • Both Arc<T> and Rc<T> are multithread safe.
  • Rc<T>

Rust book reference

Q25. Which types are not allowed within an enum variant’s body?

  • zero-sized types
  • structs
  • trait objects
  • floating-point numbers

Reference

Q26. Which statement about this code is true?

fn main() {
    let c = 'z';
    let heart_eyed_cat = '😻';
}
  • Both are character literals.
  • heart_eyed_cat is an invalid expression.
  • c is a string literal and heart_eyed_cat is a character literal.
  • Both are string literals.

Reference

Q27. Your application requires a single copy of some data type T to be held in memory that can be accessed by multiple threads. What is the thread-safe wrapper type?

  • Mutex<Arc<T>>
  • Rc<Mutex<T>>
  • Arc<Mutex<T>>
  • Mutex<Rc<T>>

Rust book reference

Q28. Which idiom can be used to concatenate the strings a, b, c?

let a = "a".to_string();
let b = "b".to_string();
let c = "c".to_string();
  • String::from(a,b,c)
  • format!("{}{}{}", a, b, c)
  • concat(a,b,c)
  • a + b + c

Q29. In this function. what level of access is provided to the variable a?

use std::fmt::Debug;

fn report<T:Debug>(a: &T) {
    eprintln!("info: {:?}", a);
}
  • print
  • read-only
  • read/write
  • debug

Q30. Which choice is not valid loop syntax?

  • loop
  • for
  • while
  • do

Q31. How do you construct a value of Status that is initialized to Waiting?

enum Status {
    Waiting,
    Busy,
    Error(String),
}
  • let s = Enum::new(Status::Waiting);
  • let s = new Status::Waiting;
  • let s = Status::Waiting;
  • let s = Status::new(Waiting);

Q32. Which statement about enums is false?

  • Enums are useful in matching patterns.
  • Option is an enum type.
  • Enum variants can have different types with associated data.
  • the term enum is short for enummap

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