Support for custom builder methods

lib/dry/types.rb

@@ -36,7 +36,7 @@ module Types
 
     # @see Dry.Types
     def self.module(*namespaces, default: :nominal, **aliases)
-      Module.new(container, *namespaces, default: default, **aliases)
+      ::Module.new(container, *namespaces, default: default, **aliases)
     end
     deprecate_class_method :module, message: <<~DEPRECATION
       Use Dry.Types() instead. Beware, it exports strict types by default, for old behavior use Dry.Types(default: :nominal). See more options in the changelog
@@ -129,22 +129,49 @@ def self.identifier(klass)
     #
     # @api private
     def self.type_map
-      @type_map ||= Concurrent::Map.new
+      @type_map ||= ::Concurrent::Map.new
     end
 
     # @api private
     def self.const_missing(const)
       underscored = Inflector.underscore(const)
 
       if container.keys.any? { |key| key.split(".")[0] == underscored }
-        raise NameError,
+        raise ::NameError,
               "dry-types does not define constants for default types. "\
               'You can access the predefined types with [], e.g. Dry::Types["integer"] '\
               "or generate a module with types using Dry.Types()"
       else
         super
       end
     end
+
+    # Add a new type builder method. This is a public API for defining custom
+    # type constructors
+    #
+    # @example simple custom type constructor
+    #   Dry::Types.define_builder(:or_nil) do |type|
+    #     type.optional.fallback(nil)
+    #   end
+    #
+    #   Dry::Types["integer"].or_nil.("foo") # => nil
+    #
+    # @example fallback alias
+    #   Dry::Types.define_builder(:or) do |type, fallback|
+    #     type.fallback(fallback)
+    #   end
+    #
+    #   Dry::Types["integer"].or(100).("foo") # => 100
+    #
+    # @param [Symbol] method
+    # @param [#call] block
+    #
+    # @api public
+    def self.define_builder(method, &block)
+      Builder.define_method(method) do |*args|
+        block.(self, *args)
+      end
+    end
   end
 
   # Export registered types as a module with constants

lib/dry/types/builder.rb

@@ -42,7 +42,7 @@ def |(other)
       #
       # @api public
       def optional
-        Types["strict.nil"] | self
+        Types["nil"] | self
       end
 
       # Turn a type into a constrained type

spec/dry/types_spec.rb

@@ -57,4 +57,20 @@ def self.[](value)
       }.to raise_error(NameError, /dry-types does not define constants for default types/)
     end
   end
+
+  describe ".define_builder" do
+    it "adds a new builder method" do
+      Dry::Types.define_builder(:or_nil) { |type| type.optional.fallback(nil) }
+      constructed = Dry::Types["integer"].or_nil
+
+      expect(constructed.("123")).to be_nil
+    end
+
+    it "has support for arguments" do
+      Dry::Types.define_builder(:or) { |type, fallback| type.fallback(fallback) }
+      constructed = Dry::Types["integer"].or(300)
+
+      expect(constructed.("123")).to eql(300)
+    end
+  end
 end