Feature#12217 Enumerable/Array sum

[phluid61]

Adds Enumerable#sum and Array#sum from Feature #12217.

I'm parking this PR here in its current state to encourage discussion and feedback.

[enebo]

@phluid61 I do have two questions. I suspect there are MRI tests we will now pass but I did not try it out so I don't know. Is that true? Secondly, can you check to make sure the sub is really an optional arity for Enumerable.sum?

[phluid61]

There are tests, yes:

• https://github.com/ruby/ruby/blob/trunk/test/ruby/test_array.rb#L2763
• https://github.com/ruby/ruby/blob/trunk/test/ruby/test_enum.rb#L846

I am in the process of porting them across, so I can run them and make sure it all passes.

Regarding the arity, I think so. That means that this is allowed, right?

~$ ruby -v -e 'p (-1..1).sum{1}'
ruby 2.4.0dev (2016-11-02 trunk 56546) [x86_64-linux]
3
~$ 

Or have I misunderstood what the arity means in that context in JRuby?

[enebo]

@phluid61 yeah that probably means it accepts any number of arguments. Zero would not work if it was required to be 1. sum { |a,b,c| 1 } should also work and I am sure it does based on that.

BTW we should also have those imported at test/mri/ruby/test_*.rb. We also can have excludes omitting tests in test/mri/excludes. You will see a name matching the class in those files with the method names which we will exclude (just letting you know as I do not see any excludes for test_sum).

[phluid61]

I've got my jruby branch built and executing. There are problems:

• array fails because of RbConfig::SIZEOF

~$ EXCLUDES=test/mri/excludes bin/jruby test/mri/runner.rb ruby/test_array.rb
/home/matty/ruby/jruby/test/mri/ruby/test_array.rb: no such file to load -- rbconfig/sizeof

• enum fails because of rounding. I assume this is related to "Kahan's compensated summation algorithm" used/spec'd in MRI

[55/66] TestEnumerable#test_sum = 0.02 s                                        
  3) Failure:
TestEnumerable#test_sum [/home/matty/ruby/jruby/test/mri/ruby/test_enum.rb:903]:
<100000000.00000001> expected but was
<100000000.0>.

[phluid61]

Well, that was ugly. I got MRI's enum tests to pass, and then I piggy-backed Array's implementation on it.

The spec/test coverage isn't astounding, but I'm pretty sure I understood the MRI implementation well enough to catch the edge-cases.

[phluid61]

I completely rebuilt Array#sum to better match MRI's implementation.

Then I created my own fake rbconfig/sizeof.rb so I could run MRI's Array tests. Everything seems good now, but I can't test against 'mathn' because:

$ bin/jruby -rmathn
NameError: method '/' not defined in Integer
    remove_method at org/jruby/RubyModule.java:2884
  <class:Integer> at /home/eprints/ruby/jruby/lib/ruby/stdlib/mathn.rb:68
           <main> at /home/eprints/ruby/jruby/lib/ruby/stdlib/mathn.rb:67
          require at org/jruby/RubyKernel.java:961
           (root) at /home/eprints/ruby/jruby/lib/ruby/stdlib/rubygems/core_ext/kernel_require.rb:1