From: Marc-Andre Lafortune <redmine@...>
Date: 2010-04-04T05:55:01+09:00
Subject: [ruby-core:29240] [Bug #3089] limited size for Array#combination [patch]

Bug #3089: limited size for Array#combination [patch]
http://redmine.ruby-lang.org/issues/show/3089

Author: Marc-Andre Lafortune
Status: Open, Priority: Low
Category: core, Target version: 1.9.2
ruby -v: ruby 1.9.2dev (2010-04-03 trunk 27200) [x86_64-darwin10.2.0]

I would expect the following to work, but it raises an error

  (0..100).to_a.combination(50).first(42)
   # => RangeError: too big for combination

There is a limit of 1 << 31 potential results (or 1 <<63, depending on the platform).

Since there is an explicit test for this, I learned the hard way I better ask if there is a valid reason for this artificial limit for #combination ?

If not, and unless there is objection, I'll commit the attached patch.

Note: I noticed this when implementing the block form of #product where a similar limit exists. Since #product without a block needs to return an array of this size, it is sensible that an error is raised in that case.
When an block is given, though, I didn't see why there should be a limit, so the limitation applies only to the form without a block. This does mean, though, that arr.product(...) might not behave the same as arr.to_enum(:product, ...).to_a, at least until Enumerators have a length method (see issue #2673)


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