Feature #15618: Implement Enumerator::Yielder#to_proc

• Status: Closed
• Assignee: -
• Target version: -

[knu (Akinori MUSHA)]

When writing an Enumerator block, you often want to delegate iteration to another method like this:

enum = Enumerator.new { |y|
  Dir.glob("*.rb") { |file|
    File.open(file) { |f| f.each_line { |line| y << line } }
  }
}

I think this is such a common pattern, but the { |var| y << var } part looks redundant compared to a normal iterator method being able to delegate to another method as simply as follows:

  def each(&block)
    @children.each(&block)
  end

So, I propose adding #to_proc to Yielder so you can directly pass a yielder object to another method as a block argument.

enum = Enumerator.new { |y|
  Dir.glob("*.rb") { |file|
    File.open(file) { |f| f.each_line(&y) }
  }
}

Yielder is all about yielding, so I think it's pretty obvious what it means.

[shevegen (Robert A. Heiler)]

I have no particularly strong pro or con opinion on the functionality itself.

I have only one comment about syntax, though. While { |line| y << line } }
may or may not be redundant (let's leave that open for the moment), and is
definitely longer than the other variant suggested, I think it is actually a
simpler-to-understand syntax compared to the .each_line(&y) variant.

[matz (Yukihiro Matsumoto)]

Sounds reasonable.

Matz.

[knu (Akinori MUSHA)]

• Status changed from Open to Closed

Merged with r67211.