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Wrap generators in iterables
Generator functions provide an easy way to write iterators without the protocol boilerplate. But unfortunately, they are also an iterable that returns itself.
For one-shot generators, it's fine. But this construct prevents multiple iterations over it.
Consider the following function, that gets an iterable and iterates over it twice:
const gen = function*() {
yield* [1, 2, 3];
}
const printTwice = (it) => {
console.log(Array.from(it));
console.log(Array.from(it));
};
printTwice(gen());
This prints:
[1, 2, 3]
[ ]
The second iteration returns nothing. Contrast that with a traditional Array, which is also an iterable:
printTwice([1, 2, 3]);
[1, 2, 3]
[1, 2, 3]
Multiple iterations are possible, as expected.
Wrap the generator in an iterable
To allow multiple iterations, wrap the generator function in an iterable that creates a new instance every time:
const wrapGenerator = (gen) => (...args) => ({
[Symbol.iterator]: () => gen(...args)
});
const wrappedGenerator = wrapGenerator(gen);
printTwice(wrappedGenerator());
This wrapped generator supports multiple iterations, and behaves like a normal iterable:
[1, 2, 3]
[1, 2, 3]