[ruby-core:106215] [Ruby master Feature#18357] Proposal: stop raising when block passed to IO#each_* closes the IO

Issue #18357 has been reported by georgeclaghorn (George Claghorn).

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Feature #18357: Proposal: stop raising when block passed to IO#each_* closes the IO
https://bugs.ruby-lang.org/issues/18357

* Author: georgeclaghorn (George Claghorn)
* Status: Open
* Priority: Normal
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As of #17661, all of the enumeration methods on `IO`—e.g. `each_line`, `each_byte`, `each_codepoint`—raise `IOError` when the given block closes the `IO`. For example, the following code raises an `IOError` if the peer sends a line containing only `quit`:

``` ruby
socket.each_line do |line|
  if line.casecmp?("quit\n")
    socket.puts "Goodbye"
    socket.close
  end
end
```

In this example, it’s trivial to `break` after closing the client socket. However, in real code, it’s likely that the command-handling code will be further away from the loop and unable to `break` out of the loop. Either the command-handling method and all intervening methods need to pass an indication of whether to keep reading back down the stack, or the block needs to include an explicit `break if io.closed?`.

In my experience, when I close an `IO`within a read loop, I intend to immediately stop reading as well. It would be more agreeable if `each_line` et al. simply stopped reading when the `IO` is closed in the block instead of raising `IOError`.

I recognize this may be considered a breaking change. The patch for #17661 was backported to 3.0, and `each_line` has behaved this way for longer. This may be workable as an option to the enumeration methods, but I’m not sure an option is worth its weight compared to explicit `break if io.closed?`. I’m mostly asking for a decision on whether the implicit behavior is worth changing for convenience and developer happiness (and aware the answer may be no).

I’ve attached a patch containing a sample implementation for `IO#each_line` and updated specs. I believe this change can be implemented similarly for all other enumeration methods.


---Files--------------------------------
patch.diff (1.66 KB)


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