Merge pull request #40 from v-kolesnikov/feature/constructor

Add Dry::Struct.constructor method

Author: flash-gordon

lib/dry/struct/class_interface.rb

@@ -2,6 +2,7 @@
 require 'dry/equalizer'
 
 require 'dry/struct/errors'
+require 'dry/struct/constructor'
 
 module Dry
   class Struct
@@ -120,6 +121,14 @@ def call(attributes = default_attributes)
       end
       alias_method :[], :call
 
+      # @param [#call,nil] constructor
+      # @param [Hash] options
+      # @param [#call,nil] block
+      # @return [Dry::Struct::Constructor]
+      def constructor(constructor = nil, **_options, &block)
+        Struct::Constructor.new(self, fn: constructor || block)
+      end
+
       # Retrieves default attributes from defined {.schema}.
       # Used in a {Struct} constructor if no attributes provided to {.new}
       #

lib/dry/struct/constructor.rb

@@ -0,0 +1,28 @@
+module Dry
+  class Struct
+    class Constructor
+      include Dry::Equalizer(:type)
+
+      # @return [#call]
+      attr_reader :fn
+
+      # @return [#call]
+      attr_reader :type
+
+      # @param [Struct] type
+      # @param [Hash] options
+      # @param [#call, nil] block
+      def initialize(type, options = {}, &block)
+        @type = type
+        @fn = options.fetch(:fn, block)
+      end
+
+      # @param [Object] input
+      # @return [Object]
+      def call(input)
+        type[fn[input]]
+      end
+      alias_method :[], :call
+    end
+  end
+end

spec/shared/struct.rb

@@ -90,6 +90,12 @@
       end
     end
 
+    describe '.constructor' do
+      it 'uses constructor function to process input' do
+        expect(type.constructor(&:to_h)[jane.to_a]).to be_eql type[jane]
+      end
+    end
+
     describe '.default?' do
       it 'is not a default' do
         expect(type).not_to be_default