override toIterable more and use it #3967
Merged
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Noticed this in #2363
We have toIterable in Foldable, but most structures were not overriding it.
Here I do that, and also use it in preference to foldRight for some default implementations in Foldable since foldRight is fundamentally hard to optimize due to the reliance on
Eval[A]
. By contrast, many things can implementtoIterable
very cheaply and we can very safely use local mutability(via .iterator)
to reduce trampolining via Eval.