Extract ExceedsMaxError as TooManyCellsError

[reshleman]

As a follow-up to df53d9a, this commit
extracts Roo::Excelx::ExceedsMaxError into a class that inherits from
Roo::Error.

The new class is renamed as Roo::TooManyCellsError in order to clarify
which maximum is being exceeded.

[stevendaniels]

use fail instead of raise

fail Roo::TooManyCellsError, ....

[reshleman]

Ah, interesting - I hadn't considered the semantic difference between raise and fail before. I'll update this.

[stevendaniels]

I prefer Roo::ExceedsCellMaxError. That way the relationship between the error and the option, :cell_max is a bit more explicit.

@simonoff Do you think it would be better if this error class had a fixed message?

class Roo::ExceedsCellMaxError < Roo::Error
  def initialize(msg = "The file has exceeded the maximum number of cells allowed")
    super
  end
end

[reshleman]

@stevendaniels Thanks for the feedback here.

I renamed this exception because I find ExceedsCellMaxError and the name of the cell_max option to be confusing and somewhat ambiguous.

For someone who hasn't read the source, it's hard to know what "max" is referring to. Is it:

• a maximum number of cells?
• the maximum value for a cell?
• some other cell-related maximum?

Even the documentation above the initialize method is confusing from the user's point of view because it doesn't explain what to use the cell_max param for:

# optional cell_max (int) parameter for early aborting attempts to parse
# enormous documents.

If it were up to me, I'd consider renaming both the exception and the name of the param to be more intention-revealing.

Just my opinion, though. I'm happy to adjust the PR if you'd prefer to keep the existing name.

[reshleman]

I also agree that it makes sense for the exception to match the name of the parameter, though.

[stevendaniels]

@reshleman

You make some good points. I agree with you: the names of both the class and the option are a bit ambiguous.

Maybe something like ExceedsMaxCellCountError would be better. It could be paired up with an option called max_cell_count. Obviously I will need to spend more time thinking about an appropriate name for both.