RUBY-1019: Document strings don't need conversion on deserialization

lib/bson/document.rb

@@ -79,7 +79,7 @@ def []=(key, value)
     # @since 3.0.0
     def initialize(elements = nil)
       super()
-      (elements || {}).each_pair{ |key, value| self[key] = value }
+      elements.each{ |key, value| self[key] = value } if elements
     end
 
     # Merge this document with another document, returning a new document in

lib/bson/hash.rb

@@ -72,11 +72,11 @@ module ClassMethods
       #
       # @since 2.0.0
       def from_bson(bson)
-        hash = new
+        hash = allocate
         bson.read(4) # Swallow the first four bytes.
         while (type = bson.readbyte.chr) != NULL_BYTE
           field = bson.gets(NULL_BYTE).from_bson_string.chop!
-          hash[field] = BSON::Registry.get(type).from_bson(bson)
+          hash.store(field, BSON::Registry.get(type).from_bson(bson))
         end
         hash
       end

perf/bench.rb

@@ -145,5 +145,15 @@ def benchmark!
     bench.report("Time#from_bson -------->") do
       count.times { Time.from_bson(StringIO.new(time_bytes)) }
     end
+
+    doc = BSON::Document.new(
+      _id: 1, name: "embedded-485", uat: Time.now, tp: "embedded", ct: 485
+    )
+    refs = 100.times.map { |i| { _id: i, n: "embed-#{i}", v: i }}
+    doc[:refs] = refs
+    doc_bytes = doc.to_bson
+    bench.report("Document#from_bson ---->") do
+      10_000.times { BSON::Document.from_bson(StringIO.new(doc_bytes)) }
+    end
   end
 end

perf/test.rb

@@ -0,0 +1,8 @@
+class MyClass
+
+  def initialize
+    10000000.times { |i| p i }
+  end
+end
+
+MyClass.new