Reference Material

Iterator Methods and Adapters

• next(&mut self) -> Option<Self::Item> Get the next element of an iterator (None if there isn't one)
• collect<B>(self) -> B -> Transforms the iterator into a collection of type B
• take(n: usize) -> Take<Self> -> Take first N elements of an iterator and turn them into an iterator
• skip(n: usize) -> Skip<Self> -> Skip first N elements of an iterator and turn them into an iterator
• cycle() -> Cycle<Self> -> Turn a finite iterator into an infinite one that repeats itself
• for_each(|x| ...) -> () -> Apply a closure to each element in the iterator
• filter(|x| ...) -> Filter<Self, P> -> Create new iterator from old one for elements where closure is true
• map(|x| ...) -> Map<Self, F> -> Create new iterator by applying closure to input iterator
• any(|x| ...) -> bool -> Return true if closure is true for any element of the iterator
• fold(init: B, |acc, x| ...) -> B -> Initialize accumulator to init, execute closure on each element
• reduce(|acc, x| ...) -> Option<Self::Item> -> Similar to fold but the initial value is the first element
• zip(other_iter) -> Zip<Self, U> -> Zip two iterators together into pairs of (a, b)
• enumerate() -> Enumerate<Self> -> Create iterator of (index, element) pairs
• partition(|x| ...) -> (B, B) -> Split iterator into two collections based on predicate
• sum() -> S -> Sum all elements (works on numeric iterators)
• count() -> usize -> Count the number of elements in the iterator
• copied() -> Copied<Self> -> Create iterator of owned copies from an iterator of references
• find(|x| ...) -> Option<Self::Item> -> Return the first element for which the closure is true (None if none)

String and &str Methods

• s.len() -> usize -> Number of bytes in the string
• s.contains("sub") -> bool -> true if string contains the substring
• s.to_uppercase() -> String -> Returns a new String in uppercase
• s.to_lowercase() -> String -> Returns a new String in lowercase
• s.push('c') -> () -> Append a single character (mutates String)
• s.push_str("text") -> () -> Append a string slice (mutates String)
• s.chars() -> Chars<'_> -> Iterator over the characters of the string
• s.split_whitespace() -> SplitWhitespace<'_> -> Iterator of substrings split by whitespace
• s.parse::<T>() -> Result<T, T::Err> -> Parse the string into type T
• s.is_empty() -> bool -> true if the string has length 0

Vec Methods

• v.push(val) -> () -> Append element to the end
• v.pop() -> Option<T> -> Remove and return last element
• v.get(i: usize) -> Option<&T> -> Safe bounds-checked access
• v.len() -> usize -> Number of elements
• v.is_empty() -> bool -> true if the vector has no elements
• v.iter() -> Iter<'_, T> -> Iterator of immutable references &T
• v.iter_mut() -> IterMut<'_, T> -> Iterator of mutable references &mut T
• v.into_iter() -> IntoIter<T> -> Consuming iterator of owned values T
• v.sort() -> () -> Sort in place in ascending order (requires T: Ord)
• v.sort_by(|a, b| ...) -> () -> Sort in place using a comparison closure (closure returns Ordering)
• v.sort_by_key(|x| ...) -> () -> Sort in place using a key function
• v.contains(&x) -> bool -> true if the vector contains x (O(n) linear scan)
• v.to_vec() -> Vec<T> -> Copy a slice &[T] into a new Vec<T> (requires T: Clone)

Option Methods

• opt.unwrap() -> T -> Extract the value or panic if None
• opt.unwrap_or(default: T) -> T -> Extract the value or return default (eager)
• opt.unwrap_or_else(|| ...) -> T -> Extract the value or compute default via closure (lazy)
• opt.map(|x| ...) -> Option<U> -> Transform the inner value; None stays None
• opt.is_some() -> bool -> true if Some
• opt.is_none() -> bool -> true if None

Other Useful Methods

• val.clone() -> T -> Create a deep copy of the value
• a.cmp(&b) -> std::cmp::Ordering -> Compare two values; returns Ordering::Less, Equal, or Greater
• ordering.then(other: Ordering) -> Ordering -> Use other as a tiebreaker when ordering is Equal (e.g. a.cmp(&b).then(x.cmp(&y)))
• val.into() -> U -> Convert val into type U via the Into/From trait (e.g. "text".into() produces a String)
• (x as f64).sqrt() -> f64 -> Square root of a floating-point number
• format!("...", args) -> String -> Like println! but returns a String instead of printing
• print!("...", args) -> Like println! but does not append a newline
• {:?} -> Debug format specifier (in println! / format!)
• {:.2} -> Display with 2 decimal places

Test Assertion Macros

• assert!(expr) -> () -> Pass if expr is true
• assert_eq!(a, b) -> () -> Pass if a == b; shows both values on failure
• assert_ne!(a, b) -> () -> Pass if a != b; shows both values on failure
• Assert macros can take an optional custom failure message, e.g., assert_eq!(a, b, "{} is not equal to {}", a, b).

HashMap Methods

Basic Operations:

• new(): Creates an empty HashMap.
• insert(key, value) -> Option<V>: Adds a key-value pair to the map. If the map did not have the key then None is returned, if the map did have the key the old value is returned as Some(V).
• remove(key) -> Option<V>: Removes a key-value pair from the map. If the map did not have the key then None is returned, if the map did have the key the value is returned as Some(V).
• get(key) -> Option<&V>: Returns a reference to the value in the map, if any, that is equal to the given key. Returns None if the key is not present.
• contains_key(key) -> bool: Checks if the map contains a specific key. Returns true if present, false otherwise.
• len() -> usize: Returns the number of key-value pairs in the map.
• is_empty() -> bool: Checks if the map contains no key-value pairs.
• clear(): Removes all key-value pairs from the map.
• drain(): Clears the map and returns all key-value pairs as an iterator.

Entry API:

• entry(key).or_insert(value): Returns a mutable reference to the value in the map, if any, that is equal to the given key. If the key is not present, inserts the given value and returns a mutable reference to the new value.
• entry(key).or_insert_with(|| ...): Like or_insert, but the default value is computed lazily from a closure (useful when construction is expensive, e.g. or_insert_with(Vec::new)).

Iterators and Views:

• iter(): Returns an immutable iterator over the key-value pairs in the map.
• iter_mut(): Returns a mutable iterator over the key-value pairs in the map.
• into_iter(): Returns a consuming iterator of owned (key, value) pairs (moves the map).
• keys(): Returns an iterator over the keys in the map.
• values(): Returns an iterator over the values in the map.
• values_mut(): Returns a mutable iterator over the values in the map.

Indexing:

• map[&key]: Returns a reference to the value for key. Panics if the key is absent. Use get for a non-panicking alternative.

HashSet Methods

Basic Operations:

• new(): Creates an empty HashSet.
• insert(value): Adds a value to the set. Returns true if the value was not present, false otherwise.
• remove(value): Removes a value from the set. Returns true if the value was present, false otherwise.
• contains(value): Checks if the set contains a specific value. Returns true if present, false otherwise.
• len(): Returns the number of elements in the set.
• is_empty(): Checks if the set contains no elements.
• clear(): Removes all elements from the set.
• drain(): Returns an iterator that removes all elements and yields them. The set becomes empty after this operation.

Entry API:

• entry(value).or_insert(value): Returns a mutable reference to the value in the set, if any, that is equal to the given value. If the value is not present, inserts the given value and returns a mutable reference to the new value.

Set Operations:

• union(&self, other: &HashSet<T>): Returns an iterator over the elements that are in self or other (or both).
• intersection(&self, other: &HashSet<T>): Returns an iterator over the elements that are in both self and other.
• difference(&self, other: &HashSet<T>): Returns an iterator over the elements that are in self but not in other.
• symmetric_difference(&self, other: &HashSet<T>): Returns an iterator over the elements that are in self or other, but not in both.
• is_subset(&self, other: &HashSet<T>): Checks if self is a subset of other.
• is_superset(&self, other: &HashSet<T>): Checks if self is a superset of other.
• is_disjoint(&self, other: &HashSet<T>): Checks if self has no elements in common with other.

Iterators and Views:

• iter(): Returns an immutable iterator over the elements in the set.
• get(value): Returns a reference to the value in the set, if any, that is equal to the given value.

BTreeMap Methods

Basic Operations:

• new(): Creates an empty BTreeMap.
• insert(key, value) -> Option<V>: Adds a key-value pair to the map. If the map did not have the key then None is returned, if the map did have the key the old value is returned as Some(V).
• remove(key) -> Option<V>: Removes a key-value pair from the map. If the map did not have the key then None is returned, if the map did have the key the value is returned as Some(V).
• get(key) -> Option<&V>: Returns a reference to the value in the map, if any, that is equal to the given key. Returns None if the key is not present.
• contains_key(key) -> bool: Checks if the map contains a specific key. Returns true if present, false otherwise.
• len() -> usize: Returns the number of key-value pairs in the map.
• is_empty() -> bool: Checks if the map contains no key-value pairs.
• clear(): Removes all key-value pairs from the map.
• drain(): Clears the map and returns all key-value pairs as an iterator.

Entry API:

• entry(key).or_insert(value): Returns a mutable reference to the value in the map, if any, that is equal to the given key. If the key is not present, inserts the given value and returns a mutable reference to the new value.
• entry(key).or_insert_with(|| ...): Like or_insert, but the default value is computed lazily from a closure (e.g. or_insert_with(Vec::new)).

Iterators and Views:

• iter(): Returns an immutable iterator over the key-value pairs in the map.
• iter_mut(): Returns a mutable iterator over the key-value pairs in the map.
• into_iter(): Returns a consuming iterator of owned (key, value) pairs (moves the map).
• keys(): Returns an iterator over the keys in the map.
• values(): Returns an iterator over the values in the map.
• values_mut(): Returns a mutable iterator over the values in the map.
• range(start..end): Returns an iterator over the key-value pairs in the map in the range [start, end).
• first_key_value(): Returns the first key-value pair in the map.
• last_key_value(): Returns the last key-value pair in the map.
• range(start..end): Returns an iterator over the key-value pairs in the map in the range [start, end).
• first_key_value(): Returns the first key-value pair in the map.
• last_key_value(): Returns the last key-value pair in the map.
• next(): Returns the next key-value pair in the map.
• next_back(): Returns the next key-value pair in the map in reverse order.

Indexing:

• map[&key]: Returns a reference to the value for key. Panics if the key is absent. Use get for a non-panicking alternative.

BTreeSet Methods

Basic Operations:

• new(): Creates an empty BTreeSet.
• insert(value): Adds a value to the set. Returns true if the value was not present, false otherwise.
• remove(value): Removes a value from the set. Returns true if the value was present, false otherwise.
• contains(value): Checks if the set contains a specific value. Returns true if present, false otherwise.
• len(): Returns the number of elements in the set.
• is_empty(): Checks if the set contains no elements.
• clear(): Removes all elements from the set.
• drain(): Returns an iterator that removes all elements and yields them. The set becomes empty after this operation.

Entry API:

• entry(value).or_insert(value): Returns a mutable reference to the value in the set, if any, that is equal to the given value. If the value is not present, inserts the given value and returns a mutable reference to the new value.

Set Operations:

• union(&self, other: &BTreeSet<T>): Returns an iterator over the elements that are in self or other (or both).
• intersection(&self, other: &BTreeSet<T>): Returns an iterator over the elements that are in both self and other.
• difference(&self, other: &BTreeSet<T>): Returns an iterator over the elements that are in self but not in other.
• symmetric_difference(&self, other: &BTreeSet<T>): Returns an iterator over the elements that are in self or other, but not in both.
• is_subset(&self, other: &BTreeSet<T>): Checks if self is a subset of other.
• is_superset(&self, other: &BTreeSet<T>): Checks if self is a superset of other.
• is_disjoint(&self, other: &BTreeSet<T>): Checks if self has no elements in common with other.

Iterators and Views:

• iter(): Returns an immutable iterator over the elements in the set.
• get(value): Returns a reference to the value in the set, if any, that is equal to the given value.
• range(start..end): Returns an iterator over the elements in the set in the range [start, end).
• first(): Returns the first element in the set.
• last(): Returns the last element in the set.
• next(): Returns the next element in the set.
• next_back(): Returns the next element in the set in reverse order.

BinaryHeap Methods (Max-Heap)

std::collections::BinaryHeap is a max-heap priority queue. Use std::cmp::Reverse to get a min-heap.

• new(): Creates an empty BinaryHeap.
• from(vals): Creates a BinaryHeap from an array or vector.
• from_iter(iter): Creates a BinaryHeap from an iterator.
• push(value) -> (): Inserts a value into the heap.
• pop() -> Option<T>: Removes and returns the largest element, or None if empty.
• peek() -> Option<&T>: Returns a reference to the largest element without removing it.
• len() -> usize: Number of elements.
• is_empty() -> bool: true if the heap has no elements.
• iter(): Returns an iterator over the elements in arbitrary order (not sorted).
• into_sorted_vec() -> Vec<T>: Consumes the heap and returns a Vec sorted in ascending order.

VecDeque Methods (Double-Ended Queue)

std::collections::VecDeque is a double-ended queue (ring buffer). Commonly used as a FIFO queue via push_back / pop_front.

• new(): Creates an empty VecDeque.
• push_back(value) -> (): Appends an element to the back.
• push_front(value) -> (): Prepends an element to the front.
• pop_back() -> Option<T>: Removes and returns the back element.
• pop_front() -> Option<T>: Removes and returns the front element.
• front() -> Option<&T>: Reference to the front element.
• back() -> Option<&T>: Reference to the back element.
• len() -> usize: Number of elements.
• is_empty() -> bool: true if empty.
• iter(): Iterator from front to back.

LinkedList Methods

std::collections::LinkedList is a doubly-linked list.

• new(): Creates an empty LinkedList.
• push_back(value) -> (): Appends an element to the back.
• push_front(value) -> (): Prepends an element to the front.
• pop_back() -> Option<T>: Removes and returns the back element.
• pop_front() -> Option<T>: Removes and returns the front element.
• front() -> Option<&T>: Reference to the front element.
• back() -> Option<&T>: Reference to the back element.
• len() -> usize: Number of elements.
• is_empty() -> bool: true if empty.
• iter(): Iterator from front to back.

Common Derivable Traits

Add with #[derive(...)] on a struct or enum:

• Debug: Enables formatting with {:?} in println! / format!.
• Clone: Provides .clone() to produce a deep copy.
• Copy: Value is copied (bitwise) on assignment instead of moved. Requires Clone. Only valid for types whose fields are all Copy (e.g., no String, no Vec<T>).
• PartialEq: Enables == and !=.
• Eq: Marker trait for total equality (no NaN-like values). Requires PartialEq. Needed (with Hash) for HashMap / HashSet keys.
• PartialOrd: Enables <, <=, >, >= via partial_cmp.
• Ord: Total ordering via cmp. Requires Eq and PartialOrd. Needed for BTreeMap / BTreeSet keys and BinaryHeap elements.
• Hash: Enables use as a HashMap / HashSet key. Typically combined with Eq.
• Default: Provides T::default() that returns a default value.

Example:

#![allow(unused)]
fn main() {
#[derive(Debug, Clone, PartialEq, Eq, Hash)]
struct Point { x: i32, y: i32 }
}