From e0eb0ee5940125fd786bed3dce4e12e082365917 Mon Sep 17 00:00:00 2001
From: ohbarye <over.rye@gmail.com>
Date: Wed, 3 Apr 2024 00:32:48 +0900
Subject: [PATCH 1/2] Refactor some arbitraries as MapArbitrary

---
 lib/pbt/arbitrary/arbitrary.rb                | 28 ++++++++++++++
 lib/pbt/arbitrary/arbitrary_methods.rb        | 14 +++----
 lib/pbt/arbitrary/array_arbitrary.rb          |  2 +-
 lib/pbt/arbitrary/char_arbitrary.rb           | 36 ------------------
 lib/pbt/arbitrary/choose_arbitrary.rb         |  2 +-
 lib/pbt/arbitrary/constant.rb                 |  5 +++
 lib/pbt/arbitrary/fixed_hash_arbitrary.rb     |  2 +-
 lib/pbt/arbitrary/integer_arbitrary.rb        |  2 +-
 .../{string_arbitrary.rb => map_arbitrary.rb} | 22 ++++-------
 lib/pbt/arbitrary/one_of_arbitrary.rb         |  2 +-
 lib/pbt/arbitrary/tuple_arbitrary.rb          |  2 +-
 spec/pbt/arbitrary/arbitrary_methods_spec.rb  | 21 +++++++++++
 spec/pbt/arbitrary/char_arbitrary_spec.rb     | 24 ------------
 spec/pbt/arbitrary/map_arbitrary_spec.rb      | 37 +++++++++++++++++++
 14 files changed, 111 insertions(+), 88 deletions(-)
 create mode 100644 lib/pbt/arbitrary/arbitrary.rb
 delete mode 100644 lib/pbt/arbitrary/char_arbitrary.rb
 rename lib/pbt/arbitrary/{string_arbitrary.rb => map_arbitrary.rb} (54%)
 delete mode 100644 spec/pbt/arbitrary/char_arbitrary_spec.rb
 create mode 100644 spec/pbt/arbitrary/map_arbitrary_spec.rb

diff --git a/lib/pbt/arbitrary/arbitrary.rb b/lib/pbt/arbitrary/arbitrary.rb
new file mode 100644
index 0000000..acdc509
--- /dev/null
+++ b/lib/pbt/arbitrary/arbitrary.rb
@@ -0,0 +1,28 @@
+# frozen_string_literal: true
+
+module Pbt
+  module Arbitrary
+    # @abstract
+    class Arbitrary
+      # @abstract
+      # @param rng [Random]
+      # @return [Object]
+      def generate(rng)
+        raise NotImplementedError
+      end
+
+      # @abstract
+      # @param current [Object]
+      # @return [Enumerator]
+      def shrink(current)
+        raise NotImplementedError
+      end
+
+      # @param mapper [Proc] a function to map the generated value. it's mainly used for #generate.
+      # @param unmapper [Proc] a function to unmap the generated value. it's used for #shrink.
+      def map(mapper, unmapper)
+        MapArbitrary.new(self, mapper, unmapper)
+      end
+    end
+  end
+end
diff --git a/lib/pbt/arbitrary/arbitrary_methods.rb b/lib/pbt/arbitrary/arbitrary_methods.rb
index 11743cd..8f2010b 100644
--- a/lib/pbt/arbitrary/arbitrary_methods.rb
+++ b/lib/pbt/arbitrary/arbitrary_methods.rb
@@ -1,14 +1,14 @@
 # frozen_string_literal: true
 
+require "pbt/arbitrary/arbitrary"
 require "pbt/arbitrary/constant"
 require "pbt/arbitrary/array_arbitrary"
-require "pbt/arbitrary/char_arbitrary"
 require "pbt/arbitrary/integer_arbitrary"
 require "pbt/arbitrary/tuple_arbitrary"
 require "pbt/arbitrary/fixed_hash_arbitrary"
 require "pbt/arbitrary/choose_arbitrary"
 require "pbt/arbitrary/one_of_arbitrary"
-require "pbt/arbitrary/string_arbitrary"
+require "pbt/arbitrary/map_arbitrary"
 
 module Pbt
   module Arbitrary
@@ -56,7 +56,7 @@ def one_of(*choices)
 
       # Generates a single unicode character (including printable and non-printable).
       def char
-        CharArbitrary.new
+        choose(0..0x10FFFF).map(CHAR_MAPPER, CHAR_UNMAPPER)
       end
 
       def alphanumeric_char
@@ -64,7 +64,7 @@ def alphanumeric_char
       end
 
       def alphanumeric_string(**kwargs)
-        StringArbitrary.new(array(alphanumeric_char, **kwargs))
+        array(alphanumeric_char, **kwargs).map(STRING_MAPPER, STRING_UNMAPPER)
       end
 
       def ascii_char
@@ -72,7 +72,7 @@ def ascii_char
       end
 
       def ascii_string(**kwargs)
-        StringArbitrary.new(array(ascii_char, **kwargs))
+        array(ascii_char, **kwargs).map(STRING_MAPPER, STRING_UNMAPPER)
       end
 
       def printable_ascii_char
@@ -80,7 +80,7 @@ def printable_ascii_char
       end
 
       def printable_ascii_string(**kwargs)
-        StringArbitrary.new(array(printable_ascii_char, **kwargs))
+        array(printable_ascii_char, **kwargs).map(STRING_MAPPER, STRING_UNMAPPER)
       end
 
       def printable_char
@@ -88,7 +88,7 @@ def printable_char
       end
 
       def printable_string(**kwargs)
-        StringArbitrary.new(array(printable_char, **kwargs))
+        array(printable_char, **kwargs).map(STRING_MAPPER, STRING_UNMAPPER)
       end
     end
   end
diff --git a/lib/pbt/arbitrary/array_arbitrary.rb b/lib/pbt/arbitrary/array_arbitrary.rb
index a23d8d9..4cede46 100644
--- a/lib/pbt/arbitrary/array_arbitrary.rb
+++ b/lib/pbt/arbitrary/array_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class ArrayArbitrary
+    class ArrayArbitrary < Arbitrary
       DEFAULT_MAX_SIZE = 10
 
       # @param min_length [Integer]
diff --git a/lib/pbt/arbitrary/char_arbitrary.rb b/lib/pbt/arbitrary/char_arbitrary.rb
deleted file mode 100644
index 7f64a2a..0000000
--- a/lib/pbt/arbitrary/char_arbitrary.rb
+++ /dev/null
@@ -1,36 +0,0 @@
-# frozen_string_literal: true
-
-module Pbt
-  module Arbitrary
-    class CharArbitrary
-      def initialize
-        @arb = ChooseArbitrary.new(0..0x10FFFF)
-      end
-
-      # @return [String]
-      def generate(rng)
-        map(@arb.generate(rng))
-      end
-
-      # Shrinks towards characters with lower codepoints, e.g. ASCII
-      # @return [Enumerator]
-      def shrink(current)
-        Enumerator.new do |y|
-          @arb.shrink(unmap(current)).each do |v|
-            y << map(v)
-          end
-        end
-      end
-
-      private
-
-      def map(v)
-        [v].pack("U")
-      end
-
-      def unmap(v)
-        v.unpack1("U")
-      end
-    end
-  end
-end
diff --git a/lib/pbt/arbitrary/choose_arbitrary.rb b/lib/pbt/arbitrary/choose_arbitrary.rb
index 93a3de4..9e297e9 100644
--- a/lib/pbt/arbitrary/choose_arbitrary.rb
+++ b/lib/pbt/arbitrary/choose_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class ChooseArbitrary
+    class ChooseArbitrary < Arbitrary
       # @param range [Range<Integer>]
       def initialize(range)
         @range = range
diff --git a/lib/pbt/arbitrary/constant.rb b/lib/pbt/arbitrary/constant.rb
index be04ab4..5e6c043 100644
--- a/lib/pbt/arbitrary/constant.rb
+++ b/lib/pbt/arbitrary/constant.rb
@@ -11,5 +11,10 @@ module Arbitrary
       *("\u{E000}".."\u{FFFD}"),
       *("\u{10000}".."\u{10FFFF}")
     ].freeze
+
+    CHAR_MAPPER = ->(v) { [v].pack("U") }
+    CHAR_UNMAPPER = ->(v) { v.unpack1("U") }
+    STRING_MAPPER = ->(v) { v.join }
+    STRING_UNMAPPER = ->(v) { v.chars }
   end
 end
diff --git a/lib/pbt/arbitrary/fixed_hash_arbitrary.rb b/lib/pbt/arbitrary/fixed_hash_arbitrary.rb
index 0f337ff..4b8897f 100644
--- a/lib/pbt/arbitrary/fixed_hash_arbitrary.rb
+++ b/lib/pbt/arbitrary/fixed_hash_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class FixedHashArbitrary
+    class FixedHashArbitrary < Arbitrary
       # @param hash [Hash<Symbol->Pbt::Arbitrary>]
       def initialize(hash)
         @keys = hash.keys
diff --git a/lib/pbt/arbitrary/integer_arbitrary.rb b/lib/pbt/arbitrary/integer_arbitrary.rb
index bff0527..230c976 100644
--- a/lib/pbt/arbitrary/integer_arbitrary.rb
+++ b/lib/pbt/arbitrary/integer_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class IntegerArbitrary
+    class IntegerArbitrary < Arbitrary
       DEFAULT_TARGET = 0
       DEFAULT_SIZE = 1000000
 
diff --git a/lib/pbt/arbitrary/string_arbitrary.rb b/lib/pbt/arbitrary/map_arbitrary.rb
similarity index 54%
rename from lib/pbt/arbitrary/string_arbitrary.rb
rename to lib/pbt/arbitrary/map_arbitrary.rb
index 5d5a18d..10e391c 100644
--- a/lib/pbt/arbitrary/string_arbitrary.rb
+++ b/lib/pbt/arbitrary/map_arbitrary.rb
@@ -2,35 +2,27 @@
 
 module Pbt
   module Arbitrary
-    class StringArbitrary
+    class MapArbitrary < Arbitrary
       # @param arb [ArrayArbitrary]
-      def initialize(arb)
+      def initialize(arb, mapper, unmapper)
         @arb = arb
+        @mapper = mapper
+        @unmapper = unmapper
       end
 
       # @return [Array]
       def generate(rng)
-        map(@arb.generate(rng))
+        @mapper.call(@arb.generate(rng))
       end
 
       # @return [Enumerator]
       def shrink(current)
         Enumerator.new do |y|
-          @arb.shrink(unmap(current)).each do |v|
-            y.yield map(v)
+          @arb.shrink(@unmapper.call(current)).each do |v|
+            y.yield @mapper.call(v)
           end
         end
       end
-
-      private
-
-      def map(v)
-        v.join
-      end
-
-      def unmap(v)
-        v.chars
-      end
     end
   end
 end
diff --git a/lib/pbt/arbitrary/one_of_arbitrary.rb b/lib/pbt/arbitrary/one_of_arbitrary.rb
index f9b1dec..75df9f9 100644
--- a/lib/pbt/arbitrary/one_of_arbitrary.rb
+++ b/lib/pbt/arbitrary/one_of_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class OneOfArbitrary
+    class OneOfArbitrary < Arbitrary
       # @param choices [Array]
       def initialize(choices)
         @choices = choices
diff --git a/lib/pbt/arbitrary/tuple_arbitrary.rb b/lib/pbt/arbitrary/tuple_arbitrary.rb
index 685133d..fff4f30 100644
--- a/lib/pbt/arbitrary/tuple_arbitrary.rb
+++ b/lib/pbt/arbitrary/tuple_arbitrary.rb
@@ -2,7 +2,7 @@
 
 module Pbt
   module Arbitrary
-    class TupleArbitrary
+    class TupleArbitrary < Arbitrary
       # @param arbs [Array<Pbt::Arbitrary>]
       def initialize(*arbs)
         @arbs = arbs
diff --git a/spec/pbt/arbitrary/arbitrary_methods_spec.rb b/spec/pbt/arbitrary/arbitrary_methods_spec.rb
index 13c048b..bf251dc 100644
--- a/spec/pbt/arbitrary/arbitrary_methods_spec.rb
+++ b/spec/pbt/arbitrary/arbitrary_methods_spec.rb
@@ -1,6 +1,27 @@
 # frozen_string_literal: true
 
 RSpec.describe Pbt::Arbitrary::ArbitraryMethods do
+  describe ".char" do
+    it "generates a character" do
+      val = Pbt.char.generate(Random.new)
+      expect(val).to be_a(String)
+      expect(val.size).to eq(1)
+    end
+
+    describe "#shrink" do
+      it "returns an Enumerator" do
+        arb = Pbt.char
+        val = arb.generate(Random.new)
+        expect(arb.shrink(val)).to be_a(Enumerator)
+      end
+
+      it "returns an Enumerator that iterates characters shrinking towards lower codepoint" do
+        arb = Pbt.char
+        expect(arb.shrink("z").to_a).to eq ["=", "\u001F", "\u0010", "\b", "\u0004", "\u0002", "\u0001", "\u0000"]
+      end
+    end
+  end
+
   describe ".alphanumeric_char" do
     it "generates a character" do
       val = Pbt.alphanumeric_char.generate(Random.new)
diff --git a/spec/pbt/arbitrary/char_arbitrary_spec.rb b/spec/pbt/arbitrary/char_arbitrary_spec.rb
deleted file mode 100644
index 83d0ffd..0000000
--- a/spec/pbt/arbitrary/char_arbitrary_spec.rb
+++ /dev/null
@@ -1,24 +0,0 @@
-# frozen_string_literal: true
-
-RSpec.describe Pbt::Arbitrary::CharArbitrary do
-  describe "#generate" do
-    it "generates an character" do
-      val = Pbt::Arbitrary::CharArbitrary.new.generate(Random.new)
-      expect(val).to be_a(String)
-      expect(val.size).to eq(1)
-    end
-  end
-
-  describe "#shrink" do
-    it "returns an Enumerator" do
-      arb = Pbt::Arbitrary::CharArbitrary.new
-      val = arb.generate(Random.new)
-      expect(arb.shrink(val)).to be_a(Enumerator)
-    end
-
-    it "returns an Enumerator that iterates characters shrinking towards lower codepoint" do
-      arb = Pbt::Arbitrary::CharArbitrary.new
-      expect(arb.shrink("z").to_a).to eq ["=", "\u001F", "\u0010", "\b", "\u0004", "\u0002", "\u0001", "\u0000"]
-    end
-  end
-end
diff --git a/spec/pbt/arbitrary/map_arbitrary_spec.rb b/spec/pbt/arbitrary/map_arbitrary_spec.rb
new file mode 100644
index 0000000..d880c31
--- /dev/null
+++ b/spec/pbt/arbitrary/map_arbitrary_spec.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+RSpec.describe Pbt::Arbitrary::MapArbitrary do
+  describe "#initialize" do
+    it do
+      arb = Pbt.integer.map(->(n) { n.to_s }, ->(n) { n.to_i })
+      expect(arb).to be_a(Pbt::Arbitrary::MapArbitrary)
+    end
+  end
+
+  describe "#generate" do
+    it "generates mapped values of given arbitrary" do
+      val = Pbt.integer.map(->(n) { n.to_s }, ->(n) { n.to_i }).generate(Random.new)
+      expect(val).to be_a(String)
+    end
+  end
+
+  describe "#shrink" do
+    it "returns an Enumerator" do
+      arb = Pbt.integer.map(->(n) { n.to_s }, ->(n) { n.to_i })
+      val = arb.generate(Random.new)
+      expect(arb.shrink(val)).to be_a(Enumerator)
+    end
+
+    it "returns an Enumerator that iterates halved arrays" do
+      arb = Pbt.integer.map(->(n) { n.to_s }, ->(n) { n.to_i })
+      expect(arb.shrink("50").to_a).to eq ["25", "13", "7", "4", "2", "1", "0"]
+    end
+
+    context "when current value and target is same" do
+      it "returns an empty Enumerator" do
+        arb = Pbt.integer.map(->(n) { n.to_s }, ->(n) { n.to_i })
+        expect(arb.shrink("0").to_a).to eq []
+      end
+    end
+  end
+end

From f14182c545e73bf02c590cf933c0f10adf94d45b Mon Sep 17 00:00:00 2001
From: ohbarye <over.rye@gmail.com>
Date: Wed, 3 Apr 2024 01:01:41 +0900
Subject: [PATCH 2/2] Implement FilterArbitrary

---
 lib/pbt/arbitrary/arbitrary.rb              |  5 +++
 lib/pbt/arbitrary/arbitrary_methods.rb      |  1 +
 lib/pbt/arbitrary/filter_arbitrary.rb       | 36 ++++++++++++++++++++
 spec/pbt/arbitrary/filter_arbitrary_spec.rb | 37 +++++++++++++++++++++
 4 files changed, 79 insertions(+)
 create mode 100644 lib/pbt/arbitrary/filter_arbitrary.rb
 create mode 100644 spec/pbt/arbitrary/filter_arbitrary_spec.rb

diff --git a/lib/pbt/arbitrary/arbitrary.rb b/lib/pbt/arbitrary/arbitrary.rb
index acdc509..fec10bd 100644
--- a/lib/pbt/arbitrary/arbitrary.rb
+++ b/lib/pbt/arbitrary/arbitrary.rb
@@ -23,6 +23,11 @@ def shrink(current)
       def map(mapper, unmapper)
         MapArbitrary.new(self, mapper, unmapper)
       end
+
+      # @param refinement [Proc] a function to filter the generated value and shrunken values.
+      def filter(&refinement)
+        FilterArbitrary.new(self, &refinement)
+      end
     end
   end
 end
diff --git a/lib/pbt/arbitrary/arbitrary_methods.rb b/lib/pbt/arbitrary/arbitrary_methods.rb
index 8f2010b..34f2595 100644
--- a/lib/pbt/arbitrary/arbitrary_methods.rb
+++ b/lib/pbt/arbitrary/arbitrary_methods.rb
@@ -9,6 +9,7 @@
 require "pbt/arbitrary/choose_arbitrary"
 require "pbt/arbitrary/one_of_arbitrary"
 require "pbt/arbitrary/map_arbitrary"
+require "pbt/arbitrary/filter_arbitrary"
 
 module Pbt
   module Arbitrary
diff --git a/lib/pbt/arbitrary/filter_arbitrary.rb b/lib/pbt/arbitrary/filter_arbitrary.rb
new file mode 100644
index 0000000..0a5b922
--- /dev/null
+++ b/lib/pbt/arbitrary/filter_arbitrary.rb
@@ -0,0 +1,36 @@
+# frozen_string_literal: true
+
+module Pbt
+  module Arbitrary
+    class FilterArbitrary < Arbitrary
+      # @param arb [ArrayArbitrary]
+      # @param refinement [Proc] a function to filter the generated value and shrunken values.
+      #
+      def initialize(arb, &refinement)
+        @arb = arb
+        @refinement = refinement
+      end
+
+      # @return [Array]
+      def generate(rng)
+        loop do
+          val = @arb.generate(rng)
+          return val if @refinement.call(val)
+        end
+      end
+
+      # @return [Enumerator]
+      def shrink(current)
+        Enumerator.new do |y|
+          @arb.shrink(current).each do |v|
+            if @refinement.call(v)
+              y.yield v
+            else
+              next
+            end
+          end
+        end
+      end
+    end
+  end
+end
diff --git a/spec/pbt/arbitrary/filter_arbitrary_spec.rb b/spec/pbt/arbitrary/filter_arbitrary_spec.rb
new file mode 100644
index 0000000..29f7487
--- /dev/null
+++ b/spec/pbt/arbitrary/filter_arbitrary_spec.rb
@@ -0,0 +1,37 @@
+# frozen_string_literal: true
+
+RSpec.describe Pbt::Arbitrary::FilterArbitrary do
+  describe "#initialize" do
+    it do
+      arb = Pbt.integer.filter { |n| n % 2 == 0 }
+      expect(arb).to be_a(Pbt::Arbitrary::FilterArbitrary)
+    end
+  end
+
+  describe "#generate" do
+    it "generates filtered values of given arbitrary" do
+      val = Pbt.integer.filter { |n| n % 2 == 0 }.generate(Random.new)
+      expect(val).to be_even
+    end
+  end
+
+  describe "#shrink" do
+    it "returns an Enumerator" do
+      arb = Pbt.integer.filter { |n| n % 2 == 0 }
+      val = arb.generate(Random.new)
+      expect(arb.shrink(val)).to be_a(Enumerator)
+    end
+
+    it "returns an Enumerator that iterates filtered values" do
+      arb = Pbt.integer.filter { |n| n % 2 == 0 }
+      expect(arb.shrink(50).to_a).to eq [4, 2, 0]
+    end
+
+    context "when current value and target is same" do
+      it "returns an empty Enumerator" do
+        arb = Pbt.integer.filter { |n| n % 2 == 0 }
+        expect(arb.shrink(0).to_a).to eq []
+      end
+    end
+  end
+end