Speed up digest with recursive hash

lib/sprockets/digest_utils.rb

@@ -35,6 +35,50 @@ def detect_digest_class(bytes)
       DIGEST_SIZES[bytes.bytesize]
     end
 
+    ADD_VALUE_TO_DIGEST = {
+      String     => ->(val, digest) { digest << val },
+      FalseClass => ->(val, digest) { digest << 'FalseClass'.freeze },
+      TrueClass  => ->(val, digest) { digest << 'TrueClass'.freeze  },
+      NilClass   => ->(val, digest) { digest << 'NilClass'.freeze   },
+
+      Symbol => ->(val, digest) {
+        digest << 'Symbol'.freeze
+        digest << val.to_s
+      },
+      Fixnum => ->(val, digest) {
+        digest << 'Fixnum'.freeze
+        digest << val.to_s
+      },
+      Bignum => ->(val, digest) {
+        digest << 'Bignum'.freeze
+        digest << val.to_s
+      },
+      Array => ->(val, digest) {
+        digest << 'Array'.freeze
+        val.each do |element|
+          ADD_VALUE_TO_DIGEST[element.class].call(element, digest)
+        end
+      },
+      Hash => ->(val, digest) {
+        digest << 'Hash'.freeze
+        val.sort.each do |array|
+          ADD_VALUE_TO_DIGEST[Array].call(array, digest)
+        end
+      },
+      Set => ->(val, digest) {
+        digest << 'Set'.freeze
+        ADD_VALUE_TO_DIGEST[Array].call(val.to_a, digest)
+      },
+      Encoding => ->(val, digest) {
+        digest << 'Encoding'.freeze
+        digest << val.name
+      },
+    }
+    ADD_VALUE_TO_DIGEST.default_proc = ->(_, val) {
+      raise TypeError, "couldn't digest #{ val }"
+    }
+    private_constant :ADD_VALUE_TO_DIGEST
+
     # Internal: Generate a hexdigest for a nested JSON serializable object.
     #
     # This is used for generating cache keys, so its pretty important its
@@ -45,46 +89,8 @@ def detect_digest_class(bytes)
     # Returns a String digest of the object.
     def digest(obj)
       digest = digest_class.new
-      queue  = [obj]
-
-      while queue.length > 0
-        obj = queue.shift
-        klass = obj.class
-
-        if klass == String
-          digest << obj
-        elsif klass == Symbol
-          digest << 'Symbol'
-          digest << obj.to_s
-        elsif klass == Fixnum
-          digest << 'Fixnum'
-          digest << obj.to_s
-        elsif klass == Bignum
-          digest << 'Bignum'
-          digest << obj.to_s
-        elsif klass == TrueClass
-          digest << 'TrueClass'
-        elsif klass == FalseClass
-          digest << 'FalseClass'
-        elsif klass == NilClass
-          digest << 'NilClass'.freeze
-        elsif klass == Array
-          digest << 'Array'
-          queue.concat(obj)
-        elsif klass == Hash
-          digest << 'Hash'
-          queue.concat(obj.sort)
-        elsif klass == Set
-          digest << 'Set'
-          queue.concat(obj.to_a)
-        elsif klass == Encoding
-          digest << 'Encoding'
-          digest << obj.name
-        else
-          raise TypeError, "couldn't digest #{klass}"
-        end
-      end
 
+      ADD_VALUE_TO_DIGEST[obj.class].call(obj, digest)
       digest.digest
     end