Types ​

The library defines some builtin types. They are useful to know if you want to extend the library with your custom operators.

Starter ​

Starter is used to create an iterable. A query must start with a starter operator. It is a function that has no arguments and returns an Iterable. It cannot have any arguments, since the query function cannot know what arguments it should have.

type Starter<T> = () => Iterable<T>

type Starter<T> = () => Iterable<T>

Operator ​

A function that receives an Iterable and returns another Iterable. Can be used to transform the source Iterable by any custom logic.

type Operator<T, R> = (source: Iterable<T>) => Iterable<R>

type Operator<T, R> = (source: Iterable<T>) => Iterable<R>

Finisher ​

A Finisher is a special type of Operator, that does not transform the source Iterable into another one, but rather transforms it into a single value. A finisher can only be the last operator of a query, no other operators or finishers can follow them.

type Finisher<T, R> = (source: Iterable<T>) => R

type Finisher<T, R> = (source: Iterable<T>) => R

Utility types for operators ​

EqualityCheck ​

It means a function, that receives two things, and decides whether they are considered equal. Can be used in some builtin operators and finishers to customize their behavior.

type EqualityCheck<T> = (left: T, right: T) => boolean

type EqualityCheck<T> = (left: T, right: T) => boolean

Comparator ​

A function that receives two things, and decides whether one is greater, less, or equal to the other. Can be used in some builtin operators and finishers to customize their behavior.

type Comparator<T> = (left: T, right: T) => number

type Comparator<T> = (left: T, right: T) => number

NOTE: A comparator implementation should return a negative number if the left argument is considered less than the right. It should return 0, if the two arguments are considered equal. It should return a positive number if the left argument is considered greater than the right.