Return Empty Array (Ruby)

Return empty array (Ruby)

To fix your code, change what you have to one of the following:

num.nil? || num.empty? ? [] : num.sort

num.nil? ? [] : num.sort

(num || []).sort

num.to_a.sort

The latter two convert num to an empty array if num is nil, then sort the result. See NilClass.to_a.

#scan suddenly returns an empty array

From the scan docs.

If the pattern contains no groups, each individual result consists of the matched string, $&. If the pattern contains groups, each individual result is itself an array containing one entry per group.

By adding the parentheses to the middle of your regex, you created a capturing group. Scan will return whatever that group captures. In the example you gave, it will be 'u'.

"Rahul\n \n\n \n Nov 6\n\n\n ・2 min read".scan(/\A\w+(\s|\w)\w+/) #=> [["u"]]

The group can be marked as non-capturing to return to your old implementation

"Rahul\n \n\n \n Nov 6\n\n\n ・2 min read".scan(/\A\w+(?:\s|\w)\w+/) #=> ["Rahul"]
#                                                       ^

Or you can add a named capture group to what you actually want to extract.

"Rahul\n \n\n \n Nov 6\n\n\n ・2 min read".match(/\A(?<name>\w+(\s|\w)\w+)/)[:name] #=> "Rahul"

Should Ruby method return nil or empty object

Not only in ruby but also in other languages, you should return an empty enumerable/collection. There is no need for your users to check if the return value is nil or not before doing any action, it's a waste of time.

Why does .all? return true on an empty array?

In Ruby you can never loop over an empty collection (array, hashes, etc.), so in your case your block never gets executed. And if the block never gets executed, all? returns true (there is no condition to make the result false).

Read about all? in the Ruby documentation.

You can simply achieve your goal by

  !array.empty? && array.all? { |value| value == 2 }

Slicing based on a condition, else return empty array

You can use the array's size as a fallback:

arr[(indices.max || arr.size)..-1]

Pushing objects into an array is returning an empty array

Adding an instance variable queue to the board class solved this

class Board
  def initialize(live_cell_count, queue)
    @live_cell_count = live_cell_count
    @queue = queue
  end

  def queue
    @queue
  end

Inserting queue.push(cell) in the conditional successfully appends each cell to the queue array.

def rules(cell)
    if something
      cell.queue_for_birth
      @queue.push(cell)
    else something_else
      cell.queue_for_death
      @queue.push(cell)
    end
  end

Why does Ruby Array slicing sometimes returns nil and sometimes returns empty Array?

The first parameter of Array#slice(start,length) is the place between indices where slicing should begin :

array = [1, 2, 3, 4]
# elements            : [   1   2   3   4   ]
#                         ↑   ↑   ↑   ↑   ↑
# slice start indices :   0   1   2   3   4

slice(0,_) begins left of 1, slice(3,_) begins left of 4, and slice(4,_) begins at the last possible place : right of 4.

slice(4,0) is still inside array, it's the empty Array right of 4.

slice(5,0) isn't inside array anymore, it's nil.

Split doesn't return empty string

From the docs:

If the limit parameter is omitted, trailing null fields are suppressed. If limit is a positive number, at most that number of fields will be returned (if limit is 1, the entire string is returned as the only entry in an array). If negative, there is no limit to the number of fields returned, and trailing null fields are not suppressed.

And so:

"[][][]".split("[]", -1)
# => ["", "", "", ""]

This yields four empty strings rather than your three, but if you think about it it's the only result that makes sense. If you split ,,, on each comma you would expect to get four empty strings as well, since there's one empty item "before" the first comma and one "after" the last.

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