Initial data commit

Task/Call-a-function/Ruby/call-a-function-8.rb

@@ -0,0 +1,14 @@
+class Array
+  def sum(init=0, &blk)
+    if blk
+      inject(init){|s, n| s + blk.call(n)}
+    else
+      inject(init){|s, n| s + n}
+    end
+  end
+end
+
+ary = [1,2,3,4,5]
+p ary.sum                               #=> 15
+p ary.sum(''){|n| (-n).to_s}            #=> "-1-2-3-4-5"
+p (ary.sum do |n| n * n end)            #=> 55