HashSet

A hash based set implementation. A HashSet allows adding any type as a value. The key benefit over using the standard Set class is that values are hashed by value instead of by reference. This allows two sets constructed at different times to be compared by their values. We can also add a set as a member of a superset and test whether the set is a member of the superset.

The hash key for a particular value is calculated as follows:

1. toHashKey(): If the value has a toHashKey method defined then this method is called to get the key.

2. number: If the value is a number then the value is used directly as the key.

3. string: If the value is any other type it is converted to a string and the numberic hash key is computed on the string using the hashString method of the HashSet.

The hash key for an entire set (a composite key) is calculated as follows:

let compositeKey = set.hashString(set.keys().join(''));

Usage

Adding Values

let a = new HashSet();
a.add(0); //=> true
a.add(0); //=> false
a.add(1); //=> true
a.size //=> 2

Set Operations

let a = new HashSet();
a.add(0);
a.add(1);

let b = new HashSet();
b.add(1);
b.add(2);

a.difference(b); //=> {0}

a.union(b); //=> {0, 1, 2}

a.intersection(b); //=> {1}

Set Membership

let a = new HashSet();
a.add(0);
a.add(1);

a.has(0); //=> true
a.has(5); //=> false

Super Sets

let superset = new HashSet();

let subset = new HashSet([0, 1]);
superset.add(subset);

let subsetWithSameValues = new HashSet([0, 1]);
superset.has(subsetWithSameValues); //=> true