@swim/util

Swim Util Library

The Swim Util library provides interfaces for ordering, equality, hashing, type conversions, functional maps, interpolators, scales, iterators, builders, key-value maps, caches, and assertions.

Overview

Ordering, equality, and hashing

Swim Util exports Comparable, Equals, and HashCode interfaces that can be implemented by ordered, equatable, and hash-able classes, respectively.

export interface Comparable<T> {
  compareTo(that: T): number;
}
export interface Equals {
  equals(that: unknown): boolean;
}
export interface HashCode extends Equals {
  hashCode(): number;
}

The exported Objects object supports generic comparison, equality testing, and hashing of arbitrary JavaScript values, including primitives, arrays, and objects.

Objects.compare(x: unknown, y: unknown): 0 | 1 | -1 returns the relative sort order of two comparable values. If x implements Comparable, then Objects.compare delegates to x's compareTo method. If x and y are both numbers, or both strings, they are compared lexicographically. If x and y are both arrays, then each corresponding element is compared, in turn, using Objects.compare. If x and y are both objects, then each entry is compared first by key, then by value, using Objects.compare. Values of incompatible types sort in a deterministic order based on type.

Objects.equal(x: unknown, y: unknown): boolean returns true if two values are equivalent. If x implements Equals, then Objects.equal delegates to x's equals method. If x and y are both primitives, then they are compared by value. If x and y are both arrays, then each corresponding element is tested for equality, in turn, using Objects.equal. If x and y are both objects, then each entry is tested for equality furst by key, then by value, using Objects.equal.

Objects.hash(x: unknown): number returns a consistent hash code for x. If x implements HashCode, then Objects.hash delegate's to x's hashCode method. If x is a primitive, it is hashed using the Murmur3 hashing algorithm. If x is an array, each element is hashed individually using Objects.hash, and the hash codes of all elements get mixed together. If x is an object, each entry has its key and value hashed using Objects.hash, and the hash codes of all entries get mixed together.

The exported Murmur3 object implements the 32-bit MurmurHash algorithm, version 3.

Builder interfaces

The exported Builder interface abstracts over construction of collections. And the PairBuilder interface abstracts over construction of key-value maps, and other pair-containing collections.

export interface Builder<I, O> {
  push(...inputs: I[]): void;
  build(): O;
}
export interface PairBuilder<K, V, O> {
  add(key: K, value: V): void;
  build(): O;
}

Map interfaces

Swim Util defines three key-value map interfaces: an ES6-compatible Map interface, as well as an OrderedMap interface, and a ReducedMap interface. An OrderedMap has its entries sorted by key order. A ReducedMap is an OrderedMap that memoizes partial combinations of sub-elements to support efficient, incremental reduction of continuously mutating datasets.

Assertions

The exported Assert interface provides a common API for constraint testing and contract enforcement. The exported assert singleton provides a default Assert implementation that throws AssertException on assert failure.