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require 'spec_helper'
require 'thread'
describe Immutable::List do
describe '#partition' do
it 'is lazy' do
-> { Immutable.stream { fail }.partition }.should_not raise_error
end
it 'calls the passed block only once for each item' do
count = 0
a,b = L[1, 2, 3].partition { |item| count += 1; item.odd? }
(a.size + b.size).should be(3) # force realization of lazy lists
count.should be(3)
end
# note: Lists are not as lazy as they could be!
# they always realize elements a bit ahead of the current one
it 'returns a lazy list of items for which predicate is true' do
count = 0
a,b = L[1, 2, 3, 4].partition { |item| count += 1; item.odd? }
a.take(1).should == [1]
count.should be(3) # would be 1 if lists were lazier
a.take(2).should == [1, 3]
count.should be(4) # would be 3 if lists were lazier
end
it 'returns a lazy list of items for which predicate is false' do
count = 0
a,b = L[1, 2, 3, 4].partition { |item| count += 1; item.odd? }
b.take(1).should == [2]
count.should be(4) # would be 2 if lists were lazier
b.take(2).should == [2, 4]
count.should be(4)
end
it 'calls the passed block only once for each item, even with multiple threads' do
mutex = Mutex.new
yielded = [] # record all the numbers yielded to the block, to make sure each is yielded only once
list = Immutable.iterate(0) do |n|
sleep(rand / 500) # give another thread a chance to get in
mutex.synchronize { yielded << n }
sleep(rand / 500)
n + 1
end
left, right = list.partition(&:odd?)
10.times.collect do |i|
Thread.new do
# half of the threads will consume the "left" lazy list, while half consume
# the "right" lazy list
# make sure that only one thread will run the above "iterate" block at a
# time, regardless
if i % 2 == 0
left.take(100).sum.should == 10000
else
right.take(100).sum.should == 9900
end
end
end.each(&:join)
# if no threads "stepped on" each other, the following should be true
# make some allowance for "lazy" lists which actually realize a little bit ahead:
(200..203).include?(yielded.size).should == true
yielded.should == (0..(yielded.size-1)).to_a
end
[
[[], [], []],
[[1], [1], []],
[[1, 2], [1], [2]],
[[1, 2, 3], [1, 3], [2]],
[[1, 2, 3, 4], [1, 3], [2, 4]],
[[2, 3, 4], [3], [2, 4]],
[[3, 4], [3], [4]],
[[4], [], [4]],
].each do |values, expected_matches, expected_remainder|
context "on #{values.inspect}" do
let(:list) { L[*values] }
context 'with a block' do
let(:result) { list.partition(&:odd?) }
let(:matches) { result.first }
let(:remainder) { result.last }
it 'preserves the original' do
list.should eql(L[*values])
end
it 'returns a frozen array with two items' do
result.class.should be(Array)
result.should be_frozen
result.size.should be(2)
end
it 'correctly identifies the matches' do
matches.should eql(L[*expected_matches])
end
it 'correctly identifies the remainder' do
remainder.should eql(L[*expected_remainder])
end
end
context 'without a block' do
it 'returns an Enumerator' do
list.partition.class.should be(Enumerator)
list.partition.each(&:odd?).should eql([L[*expected_matches], L[*expected_remainder]])
end
end
end
end
end
end
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