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: printf_func.go
    path of file: ./repos/mgmt/lang/core/fmt
    
    the code of the file until where you have to start completion: // Mgmt
// Copyright (C) 2013-2024+ James Shubin and the project contributors
// Written by James Shubin <james@s
    
func (obj *PrintfFunc) ArgGen(index int) (string, error) {
	if index == 0 {
		return printfArgNameFormat, nil
	}
	// TODO: if index is big enough that it would return the string in
	// `printfArgNameFormat` then we should return an error! (Nearly impossible.)
	return util.NumToAlpha(index - 1), nil
}