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: call.go
    path of file: ./repos/docker-ce/components/cli/vendor/google.golang.org/grpc
    
    the code of the file until where you have to start completion: /*
 *
 * Copyright 2014 gRPC authors.
 *
 * Licensed under the
    
func combine(o1 []CallOption, o2 []CallOption) []CallOption {
	// we don't use append because o1 could have extra capacity whose
	// elements would be overwritten, which could cause inadvertent
	// sharing (and race conditions) between concurrent calls
	if len(o1) == 0 {
		return o2
	} else if len(o2) == 0 {
		return o1
	}
	ret := make([]CallOption, len(o1)+len(o2))
	copy(ret, o1)
	copy(ret[len(o1):], o2)
	return ret
}