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  • Destructuring of generators

Destructuring of generators

# Arpad Borsos (10 years ago)

The destructuring assignment of the form [a, b, ...rest] = x accepts any kind of iterator. Which is great.

However, IteratorDestructuringAssignmentEvaluation of AssignmentRestElement is defined such that it creates a new Array and completely walks the iterator until its exhausted.

I’m not sure thats a good idea in case of generators. Of course one can easily work around that by doing [a, b] = gen; rest = gen;. But that takes away half the sweetness of the sugar :-) And the lazyness. And you can’t use that pattern inside parameters.

Also, there is the obvious problem what happens if you pass an infinite generator.

Any ideas?

# Kevin Smith (10 years ago)

I’m not sure thats a good idea in case of generators. Of course one can easily work around that by doing [a, b] = gen; rest = gen;. But that takes away half the sweetness of the sugar :-) And the lazyness. And you can’t use that pattern inside parameters.

The rest element needs to evaluate to the same kind of thing, whether the destructured object is a generator iterator or otherwise. Given all the other factors, having the rest element evaluate to an array makes the most sense to me.

Besides, it really doesn't seem that annoying to simply capture the iterator in question before destructuring it.

var iter = myGenerator(), [a, b] = iter;

function f(iter) { var [a, b] = iter; }

But if so, perhaps a future syntax addition could address that.