Scope | Ruby

File Local Variables

A lowercase or snake_case local variable is local to the file it is defined (contrary to Capitalized Modules and Classes, which are shared with other files when required).

Here, add is a local variable to add.rb file.

#
# add.rb
#
add = lambda do |acc, n|
  acc + n
end

#
# sum_arr.rb
#
require_relative 'add'

(1..5).inject(0, &add)

$ ruby -w sum_arr.rb
undefined local variable or method `add'

In this case, the add() lambda defined in add.rb will not be available in sum_arr.rb, even though the file is properly required.

We could make the lambda uppercase, then it would work:

Add = lambda ...

(1..5).inject(0, &Add)

But defining a lambda in the top level scope of a module with a Capitalized identifier does not read like idiomatic ruby code.

Perhaps making a proper module makes it a little more idiomatic:

#
# arith.md
#
module Arith
  Add = lambda do |acc, e|
    acc + e
  end
end

#
# sum_arr.rb
#
require_relative 'arith'

p (1..5).inject(0, &Arith::Add)