Bug #18771: IO.foreach/.readlines ignores the 4th positional argument

• Status: Closed
• Assignee: -
• Target version: -
• ruby -v: 3.0.3
• Backport: 2.7: UNKNOWN, 3.0: UNKNOWN, 3.1: UNKNOWN

[andrykonchin (Andrew Konchin)]

The IO.readlines method has the following signature:

readlines(name, sep, limit [, getline_args, open_args]) → array

The last arguments getline_args, open_args are accepted as keyword arguments, so there are actually 3 positional arguments - name, sep, and limit.

But if the method is called with any 4th positional argument - then it's just ignored. But I would expect an exception to be raised e.g. "ArgumentError: wrong number of arguments (given 4, expected 1..3)"

File.readlines('file.txt', "\n", 10)
=> ["abc\n", "\n", "def\n"]
File.readlines('file.txt', "\n", 10, {})
=> ["abc\n", "\n", "def\n"]
File.readlines('file.txt', "\n", 10, {chomp: true})
=> ["abc\n", "\n", "def\n"]
File.readlines('file.txt', "\n", 10, false)
=> ["abc\n", "\n", "def\n"]
File.readlines('file.txt', "\n", 10, nil)
=> ["abc\n", "\n", "def\n"]

It's relevant to the IO.foreach method as well.

Expected behavior - an ArgumentError exception to be raised.

[andrykonchin (Andrew Konchin)]

• Subject changed from IO.foreach/.readlines ignores the 4th positioned argument to IO.foreach/.readlines ignores the 4th positional argument
• Description updated (diff)

[andrykonchin (Andrew Konchin)]

• Description updated (diff)

[jeremyevans0 (Jeremy Evans)]

I've submitted a pull request to fix this: https://github.com/ruby/ruby/pull/5953

• Status changed from Open to Closed

Applied in changeset git|27eb36596a65d6bca44b4420ca6526175bf1b431.

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Stop ignoring 4th positional argument to IO.#{foreach,readlines}

Fixes [Bug #18771]