A taste of crystal language by converting a Ruby method

I recent learned crystal language because it is relatively fast with Ruby-like syntax. Although Rust is recently popular, it is too much for me to master.

To begin with, I need a method to find longest common substring between two. Here is a good start point in Ruby from Wikibooks.

class String
  def intersection(str)
    return '' if [self, str].any?(&:empty?)
    
    matrix = Array.new(self.length) { Array.new(str.length) { 0 } }
    intersection_length = 0
    intersection_end    = 0
    self.length.times do |x|
      str.length.times do |y|
        next unless self[x] == str[y]
        matrix[x][y] = 1 + (([x, y].all?(&:zero?)) ? 0 : matrix[x-1][y-1])

        next unless matrix[x][y] > intersection_length
        intersection_length = matrix[x][y]
        intersection_end    = x
      end
    end
    intersection_start = intersection_end - intersection_length + 1

    slice(intersection_start..intersection_end)
  end
end

How to translate this into crystal language ? Here is the result.

class String
  def intersection(str)
    return "" if [self, str].any?(&.empty?)
    
    matrix = Array.new(self.size) { Array.new(str.size) { 0 } }
    intersection_length = 0
    intersection_end    = 0
    self.length.times do |x|
      str.size.times do |y|
        next unless self[x] == str[y]
        matrix[x][y] = 1 + (([x, y].all?(&.zero?)) ? 0 : matrix[x-1][y-1])

        next unless matrix[x][y] > intersection_length
        intersection_length = matrix[x][y]
        intersection_end    = x
      end
    end
    intersection_start = intersection_end - intersection_length + 1

    self[intersection_start..intersection_end]
  end
end

They looks almost the same !! Here are some difference.

First, empty string in Crystal must be "", not single quotation mark.

Second, instead of &:method in Ruby, use &.method in Crystal.

Third, instead of length of string in Ruby, use size in Crystal.

Last, instead of slice in Ruby, use [] for substring in Crystal.

That’s it !! How easy it is.