Question 1

By default, how are variables declared in Rust?

Accepted Answer

In Rust, all variables are immutable by default when declared with let. This design promotes safety and concurrency by preventing accidental modifications. To make a variable mutable, explicitly use the mut keyword after let.

Question 2

What is ownership in Rust?

Accepted Answer

Ownership is a fundamental system in Rust that guarantees memory safety without a garbage collector. Each value has a single owner, and memory is automatically freed when the owner goes out of scope. This system prevents data races and use-after-free errors at compile time.

Question 3

What is a struct in Rust?

Accepted Answer

A struct in Rust is a custom data type that allows grouping multiple related values under a single name. It is similar to classes in other languages but without inheritance. Structs are fundamental for modeling structured data and are widely used throughout any Rust program.

Question 4

Which Rust type represents a value that may or may not be present?

Accepted Answer

Option<T> is an enum that can be either Some(T) containing a value, or None indicating the absence of a value. This type replaces null values found in other languages and forces the developer to explicitly handle the case where the value is absent, thus avoiding null pointer errors at runtime.

Question 5

Which trait must a type implement to be usable in a for loop in Rust?

Accepted Answer

The IntoIterator trait allows a type to be converted into an iterator. The for loop automatically calls into_iter() on the expression. Types like Vec, arrays and ranges implement this trait by default, which allows iterating over them directly with for.

Question 6

What is the primary use case for Box<T> in Rust?

Accepted Answer

Box<T> allocates data on the heap instead of the stack. This is useful for types with unknown size at compile time (recursive types), transferring ownership of large data without copying, or creating trait objects. The Box pointer itself has a fixed size on the stack.

Question 7

Which function should be used to create a new thread in Rust?

Accepted Answer

The thread::spawn function from the std::thread module creates a new execution thread. It takes a closure as parameter and returns a JoinHandle that allows waiting for the thread to finish using the join() method. This function is the main entry point for thread-based concurrent programming in Rust.

Question 8

Which keyword enables the superpowers of unsafe mode in Rust?

Accepted Answer

The unsafe keyword unlocks five capabilities forbidden in safe Rust: dereferencing raw pointers, calling unsafe functions, accessing mutable static variables, implementing unsafe traits, and accessing union fields. This block signals to the compiler that the developer takes responsibility for guaranteeing memory safety.

Question 9

What is the main difference between an associated type and a generic parameter in a trait?

Accepted Answer

An associated type allows only one trait implementation per type, while a generic parameter allows multiple implementations. With an associated type, the type is determined by the implementation itself, which simplifies type inference and avoids specifying the type at each use.

Question 10

What is a Higher-Ranked Trait Bound (HRTB) in Rust?

Accepted Answer

A Higher-Ranked Trait Bound (HRTB) allows specifying that a function or trait must work for all possible lifetimes, not just a specific one. The for<'a> syntax indicates that the bound must be satisfied for any lifetime 'a chosen by the caller. This feature is essential for closures and callbacks that need to accept references with varying lifetimes.

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