Ruby Map With Index

Ruby has a built-in helper on Enumerable called - each_with_index

# An array of fruits
fruits = ["Apple", "Banana", "Cherry", "Date"]

# Using each_with_index to print each fruit with its index
fruits.each_with_index do |fruit, index|
  puts "#{index}: #{fruit}"
end

Unfortunately, there is no equivalent for the Enumerable#map.

['a','b'].map_with_index {|item,index|} # => undefined method map_with_index'`

There are easy ways to work around this, but the cleanest is by chaining with_index to .map

fruits = ["Apple", "Banana", "Cherry", "Date"]

result = fruits.map.with_index do |fruit, index|
  "#{index}: #{fruit}"  # Format the output with index
end

Why? My guess is to keep the number of methods smaller over time. Technically each_with_index could be deprecated since Enumerable#each.with_index is available. This way, we do not need a _with_index for everything on Enermable.

(1..100)
   .select
   .with_index {|n, index| (n % 2 == 0) && (index % 5 == 0)}

# [6, 16, 26, 36, 46, 56, 66, 76, 86, 96]