Extend builder DSL to take implicit arrays and hashes

lib/keyword_builder.rb

@@ -66,22 +66,29 @@ def initialize(initial_attrs)
     @attrs = initial_attrs.dup
   end
 
-  def _set_attribute(attr, *args, &block)
+  def _set_attribute(attr, *args, **kwargs, &block)
     if attrs.has_key?(attr)
       raise BuilderError.new("Invalid builder state: #{attr} already provided")
     end
 
-    value =
-      if block_given?
-        raise ArgumentError.new('Cannot provide both immediate and block value') unless args.blank?
+    if kwargs.empty?
+      value = args.dup
 
-        block
-      elsif args.size == 1
-        args[0]
-      else
-        raise ArgumentError.new('Wrong number of arguments: expected 1 or block')
+      value << block if block_given?
+
+      if value.empty?
+        raise ArgumentError.new('Wrong number of arguments: expected at least one argument or block')
+      end
+
+      value = value[0] if value.size == 1
+    else
+      unless args.empty? && block.nil?
+        raise ArgumentError.new('Invalid arguments: cannot provide both keyword and positional arguments')
       end
 
+      value = kwargs.dup
+    end
+
     attrs[attr] = value
   end
 

spec/unit/keyword_builder_spec.rb

@@ -34,6 +34,32 @@ def initialize(a:, b:, c:)
       expect(result).to have_attributes(a: 1, b: 2, c: 3)
     end
 
+    it 'constructs an array when builder is given more than one argument' do
+      result = builder.build!(a: 1, b: 2) do
+        c(1, 2, 3)
+      end
+
+      expect(result).to have_attributes(a: 1, b: 2, c: [1, 2, 3])
+    end
+
+    it 'constructs an array when builder is given arguments and a block' do
+      p = proc { 1 }
+
+      result = builder.build!(a: 1, b: 2) do
+        c(3, &p)
+      end
+
+      expect(result).to have_attributes(a: 1, b: 2, c: [3, p])
+    end
+
+    it 'constructs an hash when builder is given keyword arguments' do
+      result = builder.build!(a: 1, b: 2) do
+        c(x: 3, y: 4)
+      end
+
+      expect(result).to have_attributes(a: 1, b: 2, c: { x: 3, y: 4 })
+    end
+
     it 'rejects arguments colliding with builder' do
       expect {
         builder.build!(a: 1, b: 2, c: 3) { a 1 }
@@ -55,10 +81,16 @@ def initialize(a:, b:, c:)
       }.to raise_error(ArgumentError, /Wrong number of arguments/)
     end
 
-    it 'requires only one argument' do
+    it 'rejects mixed keyword and positional arguments' do
       expect {
-        builder.build!(a: 1, b: 2) { c(1, 2, 3) }
-      }.to raise_error(ArgumentError, /Wrong number of arguments/)
+        builder.build!(a: 1, b: 2) { c(3, x: 4) }
+      }.to raise_error(ArgumentError, /Invalid arguments/)
+    end
+
+    it 'rejects mixed keyword and block arguments' do
+      expect {
+        builder.build!(a: 1, b: 2) { c(x: 3) { 4 } }
+      }.to raise_error(ArgumentError, /Invalid arguments/)
     end
 
     it 'rejects unknown arguments' do