Github user cloud-fan commented on the pull request:
https://github.com/apache/spark/pull/736#issuecomment-42955215
@rxin I'm sorry I didn't got a link for that, but I didn't find any
discussion about performance issue of Iterator#size, either. I just checked the
source code of Iterator and desugar scala for loop to see what happened.
`scala -Xprint:parser -e "var count = 0;for (i <- List(1,2,3).iterator)
count += 1"`
You can try it yourself, it will be translated into `var count = 0;List(1,
2, 3).iterator.foreach( i => count += 1)`
And the Iterator#foreach implementation is `{ while (hasNext) f(next()) }`,
it's same with what spark do to calculate the size of iterator.
Anyway, get size of an iterator is a basic function, it is logical to let
the language lib do it.
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