使用本机方法替换冗长的代码块（Ruby on Rails）

Question

I've been trying to learn the included methods with Rails and coming across situations where it seems like there should be better/cleaner ways of completing the same task, but I'm not sure how to improve.

The one I've hit most recently is as follows, where I have an array of hashes passed in as a parameter. If the array has less than 5 elements then I initialize elements until there are 5 total.

def do_stuff(numbers)
  raise "Maximum of 5 numbers can be defined in numbers array." if numbers.count > 5
  blank_range = (numbers.count-1)..5
  if blank_range.count > 0
    blank_range.each do |i|
      numbers[i] = {"entry" = " "}
    end
  end
end

This is a very basic example of what I'm wanting, though it's a pattern I've found myself using a few times. Is there a way of doing this built in?

Answer 1

I think method #fill is what you need. It takes three arguments - an object to append to array and a range to fill with that object.

numbers.fill({ 'entry' => ' ' }, numbers.size...5)

So { 'entry' => '' } is your object, numbers.size is a starting position and 5 is the end position.

If numbers.size is 5 it doesn't fill in anything.

http://www.ruby-doc.org/core-2.1.2/Array.html#method-i-fill

Answer 2

The Ruby documentation for the Array class would be a great place to start. There you'll find different ways to construct and manipulate arrays.

For example, to construct an array of 3 single space strings:

[" "] * 3         => [" ", " ", " "]
Array.new(3, " ") => [" ", " ", " "]

You could then use + to concatenate arrays like Array.new(3, " ") + numbers .

The Array class includes Enumeration , as does Range . When constructing an array from something else, inject can be useful.

Something like (1..3).inject(numbers) { |numbers, i| numbers.unshift(" ") } (1..3).inject(numbers) { |numbers, i| numbers.unshift(" ") }

Or maybe 3.times { numbers.unshift(" ") }