Add Hamster::Enumerable#grep_v

lib/hamster/enumerable.rb

@@ -29,6 +29,15 @@ def grep(pattern, &block)
       result
     end
 
+    # Search the collection for elements which are not `#===` to `item`. Yield
+    # them to the optional code block if provided, and return them as a new
+    # collection.
+    def grep_v(pattern, &block)
+      result = select { |item| !(pattern === item) }
+      result = result.map(&block) if block_given?
+      result
+    end
+
     # Yield all integers from 0 up to, but not including, the number of items in
     # this collection. For collections which provide indexed access, these are all
     # the valid, non-negative indices into the collection.

spec/lib/hamster/set/grep_v_spec.rb

@@ -0,0 +1,59 @@
+require "spec_helper"
+require "hamster/set"
+
+describe Hamster::Set do
+  let(:set) { S[*values] }
+
+  describe "#grep_v" do
+    let(:grep_v) { set.grep_v(String, &block) }
+
+    shared_examples "check filtered values" do
+      it "returns the filtered values" do
+        expect(grep_v).to eq(S[*filtered])
+      end
+    end
+
+    context "without a block" do
+      let(:block) { nil }
+
+      context "with an empty set" do
+        let(:values) { [] }
+        let(:filtered) { [] }
+
+        include_examples "check filtered values"
+      end
+
+      context "with a single item set" do
+        let(:values) { ["A"] }
+        let(:filtered) { [] }
+
+        include_examples "check filtered values"
+      end
+
+      context "with a single item set that doesn't contain match" do
+        let(:values) { [1] }
+        let(:filtered) { [1] }
+
+        include_examples "check filtered values"
+      end
+
+      context "with a multi-item set where one isn't a match" do
+        let(:values) { [2, "C", 4] }
+        let(:filtered) { [2, 4] }
+
+        include_examples "check filtered values"
+      end
+    end
+
+    describe "with a block" do
+      let(:block) { ->(item) { item + 100 }}
+
+      context "resulting items are processed with the block" do
+        let(:values) { [2, "C", 4] }
+        let(:filtered) { [102, 104] }
+
+        include_examples "check filtered values"
+      end
+    end
+  end
+end