Sequenceclass

Sequence of values designed to be extended that implements the full async generator protocol.

Note: while this class implements the iterator protocol, it is not a generator.

• Generators place additional constraints on the operation of an iterator.
• Key constraint is that a generator only runs one time through and keeps track of its status.
• This means when a generator throws, further requests to next() will always return done: true
• This class does not provide that guarantee or have that constraint.

The abstract base class for every sequence type. Sequence<T, R, N> implements AsyncIterator, AsyncIterable, and AsyncDisposable at once, so a single object can be iterated with for await...of, passed around as an iterable, and disposed with await using.

Unlike a generator, a Sequence places no one-shot constraint on iteration — throwing does not permanently end it. Subclasses implement the abstract next() method; return() and throw() have generator-like defaults that subclasses can override for cleanup.

Usage

Sequence is not used directly — extend it, or use a built-in subclass (DeferredSequence, ThroughSequence, LazySequence, InspectSequence). A minimal subclass only needs next():

import { Sequence } from "shelving/sequence";

class CountdownSequence extends Sequence<number, void, void> {
  constructor(private n: number) { super(); }
  async next() {
    return this.n > 0
      ? { done: false as const, value: this.n-- }
      : { done: true as const, value: undefined };
  }
}