Allow default values to be specified upon creation (#3)

Author: johansenja

Gemfile.lock

@@ -1,7 +1,7 @@
 PATH
   remote: .
   specs:
-    typed_struct (0.1.2)
+    typed_struct (0.1.3)
       rbs (~> 1.0)
 
 GEM

lib/typed_struct.rb

@@ -4,6 +4,10 @@
 require_relative "typed_struct/type_checking"
 require "rbs"
 
+def Rbs(type_str)
+  RBS::Parser.parse_type(type_str)
+end
+
 class TypedStruct < Struct
   include TypeChecking
 
@@ -13,8 +17,10 @@ class TypedStruct < Struct
   # any methods which are able to be overridden
   alias_method :__class__, :class
 
+  Options = nil
+
   class << self
-    def new(**properties)
+    def new(opts = Options.new, **properties)
       properties.each_key do |prop|
         if method_defined?(prop)
           $stdout.puts OVERRIDING_NATIVE_METHOD_MSG % [prop.inspect, caller(3).first]
@@ -28,7 +34,7 @@ def new(**properties)
         end
 
         klass.instance_eval do
-          @options = { types: properties }
+          @options = { types: properties, options: opts }
 
           define_method :[]= do |key, val|
             prop = properties[key]
@@ -51,17 +57,16 @@ def new(**properties)
 
   def initialize(**attrs)
     opts = self.__class__.options
-    opts[:types].each do |prop, expected_type|
-      passed_value = attrs[prop]
-      next if val_is_type? passed_value, expected_type
-
-      raise "Unexpected type #{passed_value.class} for #{prop.inspect} (expected #{expected_type})"
+    vals = opts[:types].to_h do |prop, expected_type|
+      value = attrs.fetch(prop, opts[:options][:default])
+      unless val_is_type? value, expected_type
+        raise "Unexpected type #{value.class} for #{prop.inspect} (expected #{expected_type})"
+      end
+      [prop, value]
     end
 
-    super
+    super **vals
   end
-end
 
-def Rbs(type_str)
-  RBS::Parser.parse_type(type_str)
+  Options = TypedStruct.new({ default: nil }, default: Rbs("untyped"))
 end

lib/typed_struct/version.rb

@@ -1,5 +1,5 @@
 # frozen_string_literal: true
 
 class TypedStruct < Struct
-  VERSION = "0.1.2"
+  VERSION = "0.1.3"
 end

spec/typed_struct_spec.rb

@@ -29,4 +29,50 @@
       expect(y.__class__).to be_an_instance_of Class
     end
   end
+
+  context "when passing options" do
+    it "allows for default values" do
+      x = TypedStruct.new(
+        TypedStruct::Options.new(default: 5),
+        int: Integer,
+        str: String,
+      )
+      y = x.new str: "abc"
+      expect(y.str).to eq "abc"
+      expect(y.int).to eq 5
+    end
+
+    it "allows anything responding to [] to be passed as options" do
+      x = TypedStruct.new(
+        { default: 3 },
+        xyz: /foobar/,
+        abc: :abc,
+      )
+      y = x.new abc: :abc, xyz: "foobarbaz"
+      expect(y.abc).to eq :abc
+      expect(y.xyz).to eq "foobarbaz"
+    end
+
+    it "breaks if a missing type and the type of the default don't match" do
+      x = TypedStruct.new(
+        TypedStruct::Options.new(default: 1),
+        int: Integer,
+        str: String,
+      )
+
+      expect { x.new(int: 4) }.to raise_error "Unexpected type Integer for :str (expected String)"
+    end
+  end
+
+  context "when no options passed" do
+    it "defaults to nil for missing properties" do
+      x = TypedStruct.new abc: Rbs("String?")
+      expect(x.new.abc).to be_nil
+    end
+
+    it "errors if the missing property cannot be nil" do
+      x = TypedStruct.new abc: Rbs("String")
+      expect { x.new }.to raise_error "Unexpected type NilClass for :abc (expected String)"
+    end
+  end
 end