Deprecate Rightiased::Left#value (fixes #42)

It only exists to make dry-monads backward-compatible with the kleisli gem.
However, it's an obvious anti-pattern that allows for writing unreliable code
though the main purprose of the gem is making code more reliable

See #42 for details

.gitignore

@@ -7,3 +7,4 @@
 /pkg/
 /spec/reports/
 /tmp/
+log/

CHANGELOG.md

@@ -7,6 +7,10 @@
 * `Either#flip` inverts an `Either` value  (flash-gordon)
 * `List#map` called without a block returns an `Enumerator` object (flash-gordon)
 
+## Deprecated
+
+* Direct accessing `value` on right-biased monads has been deprecated, use the `value!` method instead. `value!` will raise an exception if it is called on a Left/None/Failure instance (flash-gordon)
+
 [Compare v0.3.1...master](https://github.com/dry-rb/dry-monads/compare/v0.3.1...master)
 
 # v0.3.1 2017-03-18

dry-monads.gemspec

@@ -27,7 +27,7 @@ Gem::Specification.new do |spec|
   spec.require_paths = ['lib']
   spec.required_ruby_version = ">= 2.2.0"
   spec.add_dependency 'dry-equalizer'
-  spec.add_dependency 'dry-core'
+  spec.add_dependency 'dry-core', '~> 0.3', '>= 0.3.2'
 
   spec.add_development_dependency 'bundler'
   spec.add_development_dependency 'rake'

lib/dry/monads/either.rb

@@ -9,7 +9,6 @@ module Monads
     #
     # @api public
     class Either
-      include Dry::Equalizer(:right, :left)
       include Transformer
 
       attr_reader :right, :left
@@ -44,19 +43,20 @@ def monad
       # @api public
       class Right < Either
         include RightBiased::Right
+        include Dry::Equalizer(:value!)
 
-        alias value right
+        alias right value!
 
         # @param right [Object] a value in a correct state
-        def initialize(right)
-          @right = right
+        def initialize(value)
+          @value = value
         end
 
         # Apply the second function to value.
         #
         # @api public
         def either(_, f)
-          f.call(value)
+          f.(@value)
         end
 
         # Returns false
@@ -86,21 +86,21 @@ def fmap(*args, &block)
 
         # @return [String]
         def to_s
-          "Right(#{value.inspect})"
+          "Right(#{ @value.inspect })"
         end
         alias inspect to_s
 
         # @return [Maybe::Some]
         def to_maybe
-          Kernel.warn 'Right(nil) transformed to None' if value.nil?
-          Dry::Monads::Maybe(value)
+          Kernel.warn 'Right(nil) transformed to None' if @value.nil?
+          Dry::Monads::Maybe(@value)
         end
 
         # Transform to a Left instance
         #
         # @returns [Either::Left]
         def flip
-          Left.new(value)
+          Left.new(@value)
         end
       end
 
@@ -109,19 +109,23 @@ def flip
       # @api public
       class Left < Either
         include RightBiased::Left
+        include Dry::Equalizer(:left)
 
-        alias value left
+        # @api private
+        def left
+          @value
+        end
 
         # @param left [Object] a value in an error state
-        def initialize(left)
-          @left = left
+        def initialize(value)
+          @value = value
         end
 
         # Apply the first function to value.
         #
         # @api public
         def either(f, _)
-          f.call(value)
+          f.(@value)
         end
 
         # Returns true
@@ -148,7 +152,7 @@ def right?
         # @return [Object]
         def or(*args)
           if block_given?
-            yield(value, *args)
+            yield(@value, *args)
           else
             args[0]
           end
@@ -168,7 +172,7 @@ def or_fmap(*args, &block)
 
         # @return [String]
         def to_s
-          "Left(#{value.inspect})"
+          "Left(#{ @value.inspect })"
         end
         alias inspect to_s
 
@@ -181,13 +185,13 @@ def to_maybe
         #
         # @returns [Either::Left]
         def flip
-          Right.new(value)
+          Right.new(@value)
         end
 
         # @see Dry::Monads::RightBiased::Left#value_or
         def value_or(val = nil)
           if block_given?
-            yield(value)
+            yield(@value)
           else
             val
           end

lib/dry/monads/errors.rb

@@ -0,0 +1,9 @@
+module Dry
+  module Monads
+    class UnwrapError < StandardError
+      def initialize(left)
+        super("value! was called on #{ left.inspect }")
+      end
+    end
+  end
+end

lib/dry/monads/maybe.rb

@@ -1,4 +1,5 @@
 require 'dry/equalizer'
+require 'dry/core/deprecations'
 
 require 'dry/monads/right_biased'
 require 'dry/monads/transformer'
@@ -9,9 +10,10 @@ module Monads
     #
     # @api public
     class Maybe
-      include Dry::Equalizer(:value)
       include Transformer
 
+      extend Dry::Core::Deprecations[:'dry-monads']
+
       class << self
         # Wraps the given value with into a Maybe object.
         #
@@ -67,8 +69,7 @@ def monad
       # @api public
       class Some < Maybe
         include RightBiased::Right
-
-        attr_reader :value
+        include Dry::Equalizer(:value!)
 
         def initialize(value)
           raise ArgumentError, 'nil cannot be some' if value.nil?
@@ -91,7 +92,7 @@ def fmap(*args, &block)
 
         # @return [String]
         def to_s
-          "Some(#{value.inspect})"
+          "Some(#{ @value.inspect })"
         end
         alias inspect to_s
       end
@@ -102,14 +103,9 @@ def to_s
       class None < Maybe
         include RightBiased::Left
 
-        @instance = new
+        @instance = new.freeze
         singleton_class.send(:attr_reader, :instance)
 
-        # @return [nil]
-        def value
-          nil
-        end
-
         # If a block is given passes internal value to it and returns the result,
         # otherwise simply returns the parameter val.
         #
@@ -147,6 +143,17 @@ def to_s
           'None'
         end
         alias inspect to_s
+
+        # @api private
+        def eql?(other)
+          other.is_a?(None)
+        end
+        alias == eql?
+
+        # @api private
+        def hash
+          nil.hash
+        end
       end
 
       # A module that can be included for easier access to Maybe monads.

lib/dry/monads/right_biased.rb

@@ -1,12 +1,25 @@
 require 'dry/core/constants'
+require 'dry/core/deprecations'
+
+require 'dry/monads/errors'
 
 module Dry
   module Monads
     module RightBiased
+      # @api public
       module Right
         include Dry::Core::Constants
 
-        attr_reader :value
+        extend Dry::Core::Deprecations[:'dry-monads']
+
+        # Unwraps the underlying value
+        #
+        # @return [Object]
+        def value!
+          @value
+        end
+
+        deprecate :value, :value!
 
         # Calls the passed in Proc object with value stored in self
         # and returns the result.
@@ -24,18 +37,18 @@ module Right
         # @return [Object] result of calling proc or block on the internal value
         def bind(*args, **kwargs)
           if args.empty? && !kwargs.empty?
-            vargs, vkwargs = destructure(value)
+            vargs, vkwargs = destructure(@value)
             kw = [kwargs.merge(vkwargs)]
           else
-            vargs = [value]
+            vargs = [@value]
             kw = kwargs.empty? ? EMPTY_ARRAY : [kwargs]
           end
 
           if block_given?
             yield(*vargs, *args, *kw)
           else
             obj, *rest = args
-            obj.call(*vargs, *rest, *kw)
+            obj.(*vargs, *rest, *kw)
           end
         end
 
@@ -80,7 +93,7 @@ def or_fmap(*)
         #
         # @return [Object]
         def value_or(_val = nil)
-          value
+          @value
         end
 
         # Applies the stored value to the given argument if the argument has type of Right,
@@ -97,8 +110,8 @@ def value_or(_val = nil)
         #
         # @return [RightBiased::Left,RightBiased::Right]
         def apply(val)
-          unless value.respond_to?(:call)
-            raise TypeError, "Cannot apply #{ val.inspect } to #{ value.inspect }"
+          unless @value.respond_to?(:call)
+            raise TypeError, "Cannot apply #{ val.inspect } to #{ @value.inspect }"
           end
           val.fmap { |unwrapped| curry.(unwrapped) }
         end
@@ -114,7 +127,7 @@ def destructure(*args, **kwargs)
         def curry
           @curried ||=
             begin
-              func = value.is_a?(Proc) ? value : value.method(:call)
+              func = @value.is_a?(Proc) ? @value : @value.method(:call)
               seq_args = func.parameters.count { |type, _| type == :req }
               seq_args += 1 if func.parameters.any? { |type, _| type == :keyreq }
 
@@ -127,9 +140,19 @@ def curry
         end
       end
 
+      # @api public
       module Left
+        extend Dry::Core::Deprecations[:'dry-monads']
+
         attr_reader :value
 
+        deprecate :value, message: '.value is deprecated, use .value! instead'
+
+        # Raises an error on accessing internal value
+        def value!
+          raise UnwrapError.new(self)
+        end
+
         # Ignores the input parameter and returns self. It exists to keep the interface
         # identical to that of {RightBiased::Right}.
         #

lib/dry/monads/try.rb

@@ -38,7 +38,7 @@ def failure?
       #
       # @api public
       class Success < Try
-        include Dry::Equalizer(:value, :catchable)
+        include Dry::Equalizer(:value!, :catchable)
         include RightBiased::Right
 
         attr_reader :catchable
@@ -95,17 +95,17 @@ def fmap(*args, &block)
 
         # @return [Maybe]
         def to_maybe
-          Dry::Monads::Maybe(value)
+          Dry::Monads::Maybe(@value)
         end
 
         # @return [Either::Right]
         def to_either
-          Dry::Monads::Right(value)
+          Dry::Monads::Right(@value)
         end
 
         # @return [String]
         def to_s
-          "Try::Success(#{value.inspect})"
+          "Try::Success(#{ @value.inspect })"
         end
         alias inspect to_s
       end
@@ -134,7 +134,7 @@ def to_either
 
         # @return [String]
         def to_s
-          "Try::Failure(#{exception.class}: #{exception.message})"
+          "Try::Failure(#{ exception.class }: #{ exception.message })"
         end
         alias inspect to_s
 
@@ -150,7 +150,7 @@ def to_s
         # @return [Object]
         def or(*args)
           if block_given?
-            yield(value, *args)
+            yield(exception, *args)
           else
             args[0]
           end

lib/json/add/dry/monads/maybe.rb

@@ -19,7 +19,7 @@ def self.json_create(serialized)
       def as_json(*)
         {
           JSON.create_id => self.class.name,
-          value: value
+          value: none? ? nil : @value
         }
       end