Get rid of awkward proto argument to Interface.Run

service/datastore/interface.go

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 package datastore
 
 import (
         "golang.org/x/net/context"
 )
 
-// RunCB is the callback signature provided to Interface.Run
-//
-//   - obj is an object as specified by the proto argument of Run
-//   - getCursor can be invoked to obtain the current cursor.
-//
-// Return true to continue iterating through the query results, or false to stop.
-type RunCB func(obj interface{}, getCursor func() (Cursor, error)) bool
-
 // Interface is the 'user-friendly' interface to access the current filtered
 // datastore service implementation.
 //
 // Note that in exchange for userfriendliness, this interface ends up doing
 // a lot of reflection.
 //
 // Methods taking 'interface{}' objects describe what a valid type for that
 // interface are in the comments.
 //
 // Struct objects passed in will be converted to PropertyLoadSaver interfaces
@@ skipping 44 matching lines @@
         // datastore.
         //
         // Note that the behavior of transactions may change depending on what filters
         // have been installed. It's possible that we'll end up implementing things
         // like nested/buffered transactions as filters.
         RunInTransaction(f func(c context.Context) error, opts *TransactionOptions) error
 
         // Run executes the given query, and calls `cb` for each successfully
         // retrieved item.
         //
-        // proto is a prototype of the objects which will be passed to the callback.
-        // It will be used solely for type information, and the actual proto object
-        // may be zero/nil.  It must be of the form:
+        // cb is a callback function whose signature is
+        //   func(obj TYPE, getCursor CursorCB) bool
+        //
+        // Where TYPE is one of:
         //   - S or *S where S is a struct
         //   - P or *P where *P is a concrete type implementing PropertyLoadSaver
-        //   - *Key implies a keys-only query (and cb will be invoked with Key objects)
-        // Run will create a new, populated instance of proto for each call of
-        // cb. Run stops on the first error encountered.
-        Run(q Query, proto interface{}, cb RunCB) error
+        //   - Key (implies a keys-only query)
+        //
+        // Run stops on the first error encountered.
+        Run(q Query, cb interface{}) error
 
         // GetAll retrieves all of the Query results into dst.
         //
         // dst must be one of:
         //   - *[]S or *[]*S where S is a struct
         //   - *[]P or *[]*P where *P is a concrete type implementing PropertyLoadSaver
         //   - *[]Key implies a keys-only query.
         GetAll(q Query, dst interface{}) error
 
         // Get retrieves a single object from the datastore
@@ skipping 39 matching lines @@
         PutMulti(src interface{}) error
 
         // DeleteMulti removes items from the datastore.
         DeleteMulti(keys []Key) error
 
         // Raw returns the underlying RawInterface. The Interface and RawInterface may
         // be used interchangably; there's no danger of interleaving access to the
         // datastore via the two.
         Raw() RawInterface
 }