Adds Grape::ParameterTypes, but doesn't use it yet.

lib/grape.rb

@@ -22,7 +22,6 @@
 require 'active_support/core_ext/array/extract_options'
 require 'active_support/core_ext/hash/deep_merge'
 require 'active_support/dependencies/autoload'
-require 'grape/util/content_types'
 require 'multi_json'
 require 'multi_xml'
 require 'virtus'
@@ -160,6 +159,9 @@ module Presenters
   end
 end
 
+require 'grape/util/content_types'
+require 'grape/util/parameter_types'
+
 require 'grape/validations/validators/base'
 require 'grape/validations/attributes_iterator'
 require 'grape/validations/validators/allow_blank'

lib/grape/util/parameter_types.rb

@@ -0,0 +1,43 @@
+module Grape
+  module ParameterTypes
+    # Classes which we expect to be able to coerce through Virtus,
+    # or through any coercion logic built in to Grape.
+    KNOWN_TYPES = [
+      # Numerical
+      Integer,
+      Float,
+      BigDecimal,
+      Numeric,
+
+      # Data structures
+      Hash,
+      Array,
+      Set,
+
+      # Date/time
+      Date,
+      DateTime,
+      Time,
+
+      # Misc
+      Virtus::Attribute::Boolean,
+      String,
+      Symbol,
+      Rack::Multipart::UploadedFile
+    ]
+
+    # @param type [Class] type to check
+    # @returns [Boolean] whether or not the type is known
+    #   by Grape as an acceptable parameter type
+    def self.known_type?(type)
+      KNOWN_TYPES.include?(type)
+    end
+
+    # @param type [Class] type to check
+    # @returns [Boolean] whether or not the type can be used
+    #   as a custom type
+    def self.custom_type?(type)
+      !known_type?(type) && type.respond_to?(:parse)
+    end
+  end
+end

spec/grape/util/parameter_types_spec.rb

@@ -0,0 +1,36 @@
+require 'spec_helper'
+
+describe Grape::ParameterTypes do
+  class FooType
+    def self.parse
+    end
+  end
+
+  describe '::known_type?' do
+    [
+      Integer, Float, Numeric, BigDecimal,
+      Virtus::Attribute::Boolean, String, Symbol,
+      Hash, Array, Set,
+      Date, DateTime, Time
+    ].each do |type|
+      it "recognizes #{type} as a known type" do
+        expect(described_class.known_type?(type)).to be_truthy
+      end
+    end
+
+    it 'identifies unknown types' do
+      expect(described_class.known_type?(Object)).to be_falsy
+      expect(described_class.known_type?(FooType)).to be_falsy
+    end
+  end
+
+  describe '::custom_type?' do
+    it 'returns false if the type does not respond to :parse' do
+      expect(described_class.custom_type?(Object)).to be_falsy
+    end
+
+    it 'returns true if the type responds to :parse' do
+      expect(described_class.custom_type?(FooType)).to be_truthy
+    end
+  end
+end