4 comments

• 

  xertroyt

  8 months ago

  Hey, Greg, in self.build_archive_indices(entries) wouldn't this be sufficient?
  
  archives = Hash.new { [] }
  reply
• 

  sandal

  8 months ago

  Unfortunately, no, that won't work.
  
  The code you have shown will return an array, that's true, but it never assigns it to the Hash. So a new array will be built every time:
  
  >> a = Hash.new { [] }
  => {}
  >> a[:b]
  => []
  >> a[:b] << 1
  => [1]
  >> a[:b]
  => []
  
  This is why Hash.new passes the hash itself and the key in question into the block. You need to do something with that to persist any data.
  reply
• 

  xertroyt

  8 months ago

  Oh, right. You'd have to do archives[e.archive] <<= e as well.
  reply
• 

  sandal

  8 months ago

  I don't think I've ever seen anyone use <<= before, the fact that it works is basically an accident.
  
  It expands out to:
  
  obj = obj << other
  
  Which is very confusing: "Append to this object, then re-assign it"
  
  In this case, if you used that, you'd just be working around the fact that your Hash.new { .. } definition was written incorrectly.
  
  Hash.new { |h,k| h[k] = [] } is idiomatic for these purposes :)
  reply