How deeply does Kotlin in Action, 2E cover hashset?

Explains hash-first comparison and the equals/hashCode contract, then stops short of implementation internals beyond a hashCode example.

Hashset

As explained in Kotlin in Action, 2E

HashSet is a set implementation that organizes elements using hash codes for efficient membership testing.

A HashSet organizes elements by hash codes so membership checks can compare hashes before comparing values. For objects with custom equality, equals and hashCode must agree: equal objects must produce the same hash code. section 4.3.1

Equal customers in a HashSet

val processed = hashSetOf(Customer("Alice", 342562)) println(processed.contains(Customer("Alice", 342562))) // false If Customer overrides equals but not hashCode, the two equal-looking instances can have different hashes, so the set rejects the second instance. An implementation such as `override fun hashCode(): Int = name.hashCode() * 31 + postalCode` restores the contract. section 4.3.1

Kotlin provides several ways to create set implementations:

`java.util.HashSet` is represented from Kotlin as a MutableSet-compatible Java collection, without wrappers or copied data. section 8.2.3

How Kotlin in Action, 2E covers it

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Also explained in

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Fabulous Adventures in Data Structures and AlgorithmsHashSet<T> is a .NET collection type that stores unique values and supports hash-based membership and lookup operations.

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Related concepts

equality by valueuses · Equality by value is an equality semantics in which values are considered equal when they represent equivalent contents, regardless of object identity.
hash valueuses · A hash value is a deterministic, typically fixed-size value produced by applying a hash function to input data, often for lookup, comparison, identification, or integrity checking.
Mapkind of · A map is an associative data structure that stores key-value pairs and supports retrieving values by key.
setused by · A set is a collection of unique elements in which membership is determined by whether an element is present, not by duplicate occurrences.
bloom filteralternative to · A Bloom filter is a space-efficient probabilistic data structure for testing set membership that permits false positives but not false negatives.

This explainer was generated by Manning's knowledge graph from the text of Kotlin in Action, 2E. The section links point to the parts of the book it draws on.