cleanup.

lib/graphql/stitching.rb

@@ -27,18 +27,24 @@ class CompositionError < StitchingError; end
     class ValidationError < CompositionError; end
 
     class << self
-      def digest_class
-        @digest_class ||= Digest::SHA2
-      end
+      attr_writer :stitch_directive
 
-      attr_writer :digest_class
+      # Proc used to compute digests; uses SHA2 by default.
+      # @returns [Proc] proc used to compute digests.
+      def digest(&block)
+        if block_given?
+          @digest = block
+        else
+          @digest ||= ->(str) { Digest::SHA2.hexdigest(str) }
+        end
+      end
 
+      # Name of the directive used to mark type resolvers.
+      # @returns [String] name of the type resolver directive.
       def stitch_directive
         @stitch_directive ||= "stitch"
       end
 
-      attr_writer :stitch_directive
-
       # Names of stitching directives to omit from the composed supergraph.
       # @returns [Array<String>] list of stitching directive names.
       def stitching_directive_names

lib/graphql/stitching/request.rb

@@ -75,12 +75,12 @@ def normalized_string
 
       # @return [String] a digest of the original document string. Generally faster but less consistent.
       def digest
-        @digest ||= Stitching.digest_class.hexdigest("#{Stitching::VERSION}/#{string}")
+        @digest ||= Stitching.digest.call("#{Stitching::VERSION}/#{string}")
       end
 
       # @return [String] a digest of the normalized document string. Slower but more consistent.
       def normalized_digest
-        @normalized_digest ||= Stitching.digest_class.hexdigest("#{Stitching::VERSION}/#{normalized_string}")
+        @normalized_digest ||= Stitching.digest.call("#{Stitching::VERSION}/#{normalized_string}")
       end
 
       # @return [GraphQL::Language::Nodes::OperationDefinition] The selected root operation for the request.

lib/graphql/stitching/type_resolver.rb

@@ -47,7 +47,7 @@ def list?
       end
 
       def version
-        @version ||= Stitching.digest_class.hexdigest("#{Stitching::VERSION}/#{as_json.to_json}")
+        @version ||= Stitching.digest.call("#{Stitching::VERSION}/#{as_json.to_json}")
       end
 
       def ==(other)