Cop idea: Prefer first and last over [0] and [-1]

[ydakuka]

https://rubystyle.guide/#first-and-last

Describe the solution you'd like

When accessing the first or last element from an array, prefer first or last over [0] or [-1].

arr = [1, 2, 3]

# bad
arr[0]  # => 1
arr[-1] # => 3

# good
arr.first # => 1
arr.last  # => 3

Rubocop

ydakuka@yauhenid:~/Work/project$ bin/rails_docker rubocop -V
1.57.2 (using Parser 3.2.2.4, rubocop-ast 1.29.0, running on ruby 2.7.8) [x86_64-linux]
  - rubocop-capybara 2.19.0
  - rubocop-factory_bot 2.24.0
  - rubocop-performance 1.19.1
  - rubocop-rails 2.22.0
  - rubocop-rake 0.6.0
  - rubocop-rspec 2.25.0
  - rubocop-thread_safety 0.5.1

[ydakuka]

# good

def calculate_value(result, index)
  service.calculate_value(
    result[-3][index],
    result[-2][index],
    result[-1][index],
  )
end

# good

def metrics_by_type(metric_type)
  attributes
    .to_a
    .select { |metric| metric[0][0] == metric_type.first }
end