You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: windowed_wordcount.go
    path of file: ./repos/beam/sdks/go/examples/windowed_wordcount
    
    the code of the file until where you have to start completion: // Licensed to the Apache Software Foundation (ASF) under one or more
// contributor license agreements.  See the NOTICE file distributed with
// this work for additional information regarding copyright ownership.
// The ASF licenses this file
    
func init() {
	// register.DoFnXxY registers a struct DoFn so that it can be correctly serialized and does some optimization
	// to avoid runtime reflection. Since addTimestampFn has 1 inputs and 2 outputs, we use register.DoFn1x2 and provide
	// its input/output types as its constraints.
	// Struct DoFns must be registered for a pipeline to run.
	register.DoFn1x2[beam.X, beam.EventTime, beam.X](&addTimestampFn{})
	// For simple functional (non-struct) DoFns we can use register.FunctionXxY to perform the same registration without
	// providing type constraints.
	register.Function4x1(formatFn)
}