Template Class HashMap

• Defined in File hash_map.hpp

Nested Types

• Struct HashMap::Entry

template<typename Key, typename Value>
class HashMap

A hash map implementation using open addressing with linear probing.

This class provides a fixed-capacity hash map that uses pre-allocated memory and linear probing for collision resolution. It supports basic operations like insert, get, erase, and has. The hash map is designed for performance-critical scenarios where memory allocation should be minimized.

Template Parameters

• Key – The key type for the hash map.

• Value – The value type for the hash map.

Public Types

enum class Error

Error codes used by this class.

Values:

enumerator kInvalidArgument

kInvalidArgument is returned when a function is called with argument that does not make sense such as negative size or capacity smaller than size.

enumerator kOutOfMemory

kOutOfMemory is returned when a memory allocation fails.

enumerator kHashMapFull

kHashMapFull is returned if the hash map is full.

enumerator kKeyNotFound

kKeyNotFound is returned if the key is not found in the hash map.

enumerator kKeyAlreadyExists

kKeyAlreadyExists is returned if the key already exists in the hash map.

template<typename T>
using expected_t = expected<T, Error>

Expected type used by this class.

using unexpected_t = unexpected<Error>

Unexpected type used by this class.

using hash_t = uint64_t

Hash type used internally.

Public Functions

HashMap() = default

Default constructor used to be able to pre-allocate memory.

inline expected_t<void> reserve(int32_t size, int32_t capacity)

Reserve memory for the hash map.

Parameters

• size – Maximum number of elements the hash map can store.

• capacity – Total capacity of the internal array (should be larger than size for efficiency).

Returns

Success or error status.

inline bool has(const Key &key) const

Check if a key exists in the hash map.

Parameters

key – The key to search for.

Returns

True if the key exists, false otherwise.

inline expected_t<Value> get(const Key &key) const

Get the value associated with a key.

Parameters

key – The key to search for.

Returns

Value associated with the key on success, Error::kKeyNotFound if key doesn’t exist.

inline expected_t<void> insert(const Key &key, Value value)

Insert a key-value pair into the hash map.

Parameters

• key – The key to insert.

• value – The value to associate with the key.

Returns

Success or error status. Error::kHashMapFull if the map is full, Error::kKeyAlreadyExists if the key already exists.

inline expected_t<void> erase(const Key &key)

Remove a key-value pair from the hash map.

Parameters

key – The key to remove.

Returns

Success or error status. Error::kKeyNotFound if the key doesn’t exist.

inline int32_t size() const

Get the current number of elements in the hash map.

Returns

Current size of the hash map.