Feature #16913: Add `ARGF#each_io`

• Status: Open
• Assignee: -
• Target version: -

[prajjwal (Prajjwal Singh)]

Add an iterator for each file supplied on the command line, or STDIN. ARGF#each_io

Current Status

Often, we need to do something with individual files ARGF knows about rather than the concatenation of them. We can combine ARGF#to_io and ARGF#skip to achieve this as follows:

while (file = ARGF.to_io)
  break if file.closed? || file.eof?

  csv = CSV.new(file)
  csv.each { |line| p line }

  ARGF.skip
end

Proposal

Add an iterator ARGF#each_io to do the above. The above example would then become:

ARGF.each_io do |io|
  csv = CSV.new(io)

  csv.each { |line| p line }
end

The name is #each_io. We could call it #each_file as well, but ARGF#to_io emits an IO object when the current file is STDIN.

Implementation

A cursory ruby implementation is below. Could better handle the STDIN edge case, and would probably be better off being written in C.

def ARGF.each_io(&fn)
  raise 'ARGF#each_io needs a block!' unless block_given?

  while (file = to_io)
    break if file.closed? || file.eof?

    fn.call(file)

    # File was STDIN, no need to go any further.
    break if file.class == IO

    skip
  end
end

Issues

• Handling the STDIN edge case is ugly.
• Not clear if eof? checking for STDIN should be left up to the user instead.
• A real world implementation should return a proper iterator instead of the above.