Add basic array operations to Rackstash::Fields::Array

lib/rackstash/fields/array.rb

@@ -12,6 +12,46 @@ module Rackstash
         @raw = Concurrent::Array.new
       end
 
+      # @!method +(array)
+      #   Concatenation — Returns a new {Rackstash::Fields::Array} built by
+      #   concatenating `self` and  the given `array` together to produce a
+      #   third array.
+      #
+      #   @param array [::Array, Rackstash::Fields::Array]
+      #   @return [Rackstash::Fields::Array]
+
+      # @!method -(array)
+      #   Array Difference — Returns a new {Rackstash::Fields::Array} that is a
+      #   copy of `self`, removing any items that also appear in the given
+      #   `array`. The order is preserved from `self`.
+      #
+      #   @param array [::Array, Rackstash::Fields::Array]
+      #   @return [Rackstash::Fields::Array]
+
+      # @!method |(array)
+      #   Set Union — Returns a new {Rackstash::Fields::Array} by joining `self`
+      #   with the given `array`, excluding any duplicates and preserving the
+      #   order from `self`.
+      #
+      #   @param array [::Array, Rackstash::Fields::Array]
+      #   @return [Rackstash::Fields::Array]
+
+      # @!method &(array)
+      #   Set Intersection — Returns a new {Rackstash::Fields::Array} containing
+      #   elements common to `self` and the given `array`, excluding any
+      #   duplicates. The order is preserved from `self`.
+      #
+      #   @param array [::Array, Rackstash::Fields::Array]
+      #   @return [Rackstash::Fields::Array]
+
+      %i[+ - | &].each do |op|
+        class_eval <<-RUBY, __FILE__ , __LINE__ + 1
+          def #{op}(array)
+            new(@raw #{op} normalize(array, wrap: false))
+          end
+        RUBY
+      end
+
       # Retrieve a stored value from a given `index`
       #
       # @param index [Integer] the index in the array where we fetch the value
@@ -92,6 +132,13 @@ module Rackstash
         return obj.to_ary if obj.respond_to?(:to_ary)
         raise TypeError, "no implicit conversion of #{obj.class} into Array"
       end
+
+      def new(raw)
+        self.class.new.tap do |array|
+          array.raw = raw
+        end
+      end
+
     end
 
     def self.Array(array)

spec/rackstash/fields/array_spec.rb

@@ -10,6 +10,58 @@ require 'rackstash/fields/array'
 describe Rackstash::Fields::Array do
   let(:array) { Rackstash::Fields::Array.new }
 
+  describe '#+' do
+    it 'returns the addition of elements' do
+      array[0] = 'existing'
+      expect(array + ['existing', -> { 'new' }, [:nested]])
+        .to contain_exactly 'existing', 'existing', 'new', ['nested']
+    end
+
+    it 'returns a new Array' do
+      expect(array + [:foo]).to be_a(Rackstash::Fields::Array)
+      expect(array + [:foo]).not_to equal array
+    end
+  end
+
+  describe '#-' do
+    it 'returns the subtraction of elements' do
+      array[0] = 'foo'
+      array[1] = 'bar'
+      expect(array - [-> { :bar }, ['foo']]).to contain_exactly 'foo'
+    end
+
+    it 'returns a new Array' do
+      expect(array - [:foo]).to be_a(Rackstash::Fields::Array).and be_empty
+      expect(array - [:foo]).not_to equal array
+    end
+  end
+
+  describe '#|' do
+    it 'returns the union of elements' do
+      array[0] = 'existing'
+      expect(array | ['new', :existing, -> { 123 }])
+        .to contain_exactly 'existing', 'new', 123
+    end
+
+    it 'returns a new Array' do
+      expect(array | [:foo]).to be_a(Rackstash::Fields::Array)
+      expect(array | [:foo]).not_to equal array
+    end
+  end
+
+  describe '#&' do
+    it 'returns the intersection of elements' do
+      array[0] = 'existing'
+      expect(array & [:existing, 'new'])
+        .to contain_exactly 'existing'
+    end
+
+    it 'returns a new Array' do
+      expect(array & [:foo]).to be_a(Rackstash::Fields::Array).and be_empty
+      expect(array & [:foo]).not_to equal array
+    end
+  end
+
   describe '#[]' do
     it 'returns nil if a value was not set' do
       expect(array[1]).to be_nil