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Rust
Rust flash cards
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What is consistent across vtables for the same trait?
Every trait object for a given trait will have the same layout for its vtable.
What are trait objects often referred to as, and why?
Trait objects are fat pointers, containing a pointer to the data and a pointer to the vtable.fdfdf
Can function pointers capture environment variables?
No, function pointers cannot capture environment variables.
What are function pointers in Rust?
Function pointers in Rust allow you to pass functions as arguments to other functions.
Can function pointers point to unsafe functions?
Yes, function pointers can point to both safe and unsafe functions.
How can function pointer types be simplified?
This can be done using type aliases to make the code more readable.
How do you define function pointers in Rust?
You can define function pointers using the `fn` keyword.
Are function pointers compatible with closures?
Function pointers are compatible with closures that do not capture any environment variables.
What is one use case for function pointers?
Function pointers enable callbacks, allowing functions to be called when specific events occur.
What is the benefit of static dispatch?
Improves performance by eliminating runtime overhead of dynamic dispatch.
What technique does Rust use to achieve static dispatch with generics?
Monomorphization
What is a disadvantage of monomorphization?
Code bloat due to multiple copies of the same function for different types.
How does monomorphization work?
Each concrete type used with a generic function creates a new version of that function at compile time.
What is static dispatch?
A technique where the specific function to be called is determined at compile time.
What is static dispatch?
Eliminating dynamic dispatch overhead by resolving function calls at compile time.
What are virtual tables?
A technique used in object-oriented programming languages (like C++) to achieve dynamic polymorphism.
What are trait objects often referred to as, and why?
Trait objects are fat pointers, containing a pointer to the data and a pointer to the vtable.
When are vtables created?
Vtables are typically created by the compiler at compile time.
Which is generally faster, static dispatch or dynamic dispatch?
Static dispatch is generally faster because the method call is known at compile time.
How is the vtable organized?
The order of function pointers in the vtable matches the order of the methods in the trait definition.
What is consistent across vtables for the same trait?
Every trait object for a given trait will have the same layout for its vtable.
What is a performance consideration when using virtual tables?
Virtual tables incur a small runtime overhead due to the indirection of looking up method pointers.
How does dynamic dispatch (using vtables) differ from static dispatch?
Dynamic dispatch resolves method calls at runtime, while static dispatch resolves them at compile time.
What is the benefit of using virtual tables?
Virtual tables enable different types to be treated uniformly through trait objects, enhancing code flexibility.
When is dynamic dispatch necessary?
Dynamic dispatch is essential for polymorphism when the exact type is not known at compile time.
How are vtables used for dynamic dispatch?
Trait objects use vtables to call the correct method implementation at runtime, enabling polymorphism.
What two pointers does a trait object store?
Trait objects store a pointer to the data and a pointer to the vtable.
What is a virtual table (vtable)?
A mechanism that allows dynamic dispatch of methods at runtime.
What does each vtable contain?
Each type that implements the trait has its own vtable, which points to the type-specific implementations.
How is a vtable generated in Rust?
When a trait object is created, the compiler generates a vtable containing pointers to the actual implementations of the trait's methods for the concrete type.
Why are vtables needed for trait objects?
The compiler does not know the concrete type at compile time, so it uses the vtable to determine which method to call.
What is guaranteed by using Arc, Mutex, RwLock and Cells correctly in Rust?
It is not possible to have a data race.
What is a MutexGuard?
Used to access the data within a Mutex.
When is the memory associated with an `Arc` deallocated?
When the last `Arc` pointer to the allocation is dropped, the memory is freed.
What is a potential issue when using Mutex in Rust?
Potential for deadlocks if not handled carefully.
When would you use Cell<T> instead of RefCell<T>?
Used for simple cases where you need mutability without shared ownership.
When is RwLock<T> more suitable than Mutex<T>?
Useful when data is frequently read but rarely written, optimizing performance.
How do you read and write data stored in a Cell<T>?
`get()` and `set()` methods.
What is Arc (Atomically Reference Counted)?
Allows multiple owners of the same data by using reference counting. Data is immutable.
What is the primary use case for Mutex<T>?
Used when shared mutable state is needed across multiple threads.
What is RwLock (Read-Write Lock)?
Provides multiple readers or a single writer at a time.
How do you access data protected by a Mutex?
Use `lock()` to acquire the lock, which returns a `MutexGuard`.
What is a key feature of Arc<T> that enables shared ownership?
Can be cloned to provide multiple shared references to the same underlying data.
How does RefCell<T> differ from Cell<T>?
RefCell<T> provides borrowing rules checked at runtime, causing a panic if violated.
How does Rust ensure that a Mutex is eventually unlocked?
Unlocks automatically when the MutexGuard goes out of scope.
How does Cell<T> allow mutation of an immutable value?
Copy the data in and out of the Cell.
What is Mutex?
A type that provides mutually exclusive access to shared data.
How does Arc differ from Rc?
Arc<T> is similar to Rc<T>, but is safe to share across threads.
Using RwLock, how do you ensure exclusive access for writing?
Acquire a write lock with `write()` to modify the data.
In what Rust module can you find Arc, Mutex, and RwLock?
std::sync
How does RwLock prevent data corruption?
Prevents data races by ensuring only one writer at a time.
How do you access data protected by a RwLock?
`read()` for shared access, `write()` for exclusive access.
What are Cells?
Types that provide interior mutability.
What does interior mutability (provided by Cells) enable?
Allows modification of data even when there are immutable references to that data.
What is a restriction on the type `T` when using `Cell<T>`?
The data must be `Copy`.
How is the reference count in Arc incremented?
A program can use `Arc::clone()` to create another pointer to the same allocation.
What does Cell rely on internally?
Unsafe code to bypass Rust's borrowing rules at compile time.
What trait implementations are required for a type T to be safely used within an Arc?
Send + Sync
Describe the read-write access pattern enforced by RwLock.
Multiple readers can access data concurrently, but only one writer can access data exclusively.