Designing with Exceptions
If File.open succeeds, it returns {:ok, file}, where file is the service that gives you access to the file. If it fails, it returns {:error, reason}. So, for code that knows a file open might not succeed and that wants to handle the fact, you might write
| | case File.open(user_file_name) do |
| | {:ok, file} -> |
| | process(file) |
| | {:error, message} -> |
| | IO.puts :stderr, "Couldn't open #{user_file_name}: #{message}" |
| | end |
If instead you expect the file to open successfully every time, you could raise an exception on failure.
| | case File.open("config_file") do |
| | {:ok, file} -> |
| | process(file) |
| | {:error, message} -> |
| | raise "Failed to open config file: #{message}" |
| | end |
Or you could let Elixir raise an exception ...
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