Implement Array#minmax

Array#minmax was previous not implemented, so calling #minmax on
array was actually calling Enumerable#minmax.  This is a simple
implementation of #minmax by just calling rb_ary_min and
rb_ary_max, which improves performance significantly.

Fixes [Bug #15929]

array.c

@@ -4850,6 +4850,26 @@ rb_ary_min(int argc, VALUE *argv, VALUE ary)
     return result;
 }
 
+/*
+ *  call-seq:
+ *     ary.minmax                       -> [obj, obj]
+ *     ary.minmax {| a,b | block }      -> [obj, obj]
+ *
+ *  Returns a two element array which contains the minimum and the
+ *  maximum value in the array.
+ *
+ *  Can be given an optional block to override the default comparison
+ *  method <code>a <=> b</code>.
+ */
+static VALUE
+rb_ary_minmax(VALUE ary)
+{
+    if (rb_block_given_p()) {
+        return rb_call_super(0, NULL);
+    }
+    return rb_assoc_new(rb_ary_min(0, 0, ary), rb_ary_max(0, 0, ary));
+}
+
 static int
 push_value(st_data_t key, st_data_t val, st_data_t ary)
 {
@@ -6902,6 +6922,7 @@ Init_Array(void)
 
     rb_define_method(rb_cArray, "max", rb_ary_max, -1);
     rb_define_method(rb_cArray, "min", rb_ary_min, -1);
+    rb_define_method(rb_cArray, "minmax", rb_ary_minmax, 0);
 
     rb_define_method(rb_cArray, "uniq", rb_ary_uniq, 0);
     rb_define_method(rb_cArray, "uniq!", rb_ary_uniq_bang, 0);

test/ruby/test_array.rb

@@ -1792,6 +1792,25 @@ class TestArray < Test::Unit::TestCase
     assert_same(obj, [obj, 1.0].max)
   end
 
+  def test_minmax
+    assert_equal([1, 3], [1, 2, 3, 1, 2].minmax)
+    assert_equal([3, 1], [1, 2, 3, 1, 2].minmax {|a,b| b <=> a })
+    cond = ->((a, ia), (b, ib)) { (b <=> a).nonzero? or ia <=> ib }
+    assert_equal([[3, 2], [1, 3]], [1, 2, 3, 1, 2].each_with_index.minmax(&cond))
+    ary = %w(albatross dog horse)
+    assert_equal(["albatross", "horse"], ary.minmax)
+    assert_equal(["dog", "albatross"], ary.minmax {|a,b| a.length <=> b.length })
+    assert_equal([1, 3], [3,2,1].minmax)
+
+    class << (obj = Object.new)
+      def <=>(x) 1 <=> x end
+      def coerce(x) [x, 1] end
+    end
+    ary = [obj, 1.0].minmax
+    assert_same(obj, ary[0])
+    assert_equal(obj, ary[1])
+  end
+
   def test_uniq
     a = []
     b = a.uniq