It’s possible to implement an each method in a class mixing in
Enumerable that runs forever, and thus causing, for example, to_a to run
forever. One such class is mathn’s Prime class:
require ‘mathn’
Prime.new.to_a # ← runs forever, never returns
This seems a bit broken to me, and I was writing a program where I
needed the first n primes, or all the primes under 200, for example, so
I re-wrote Enumerable#to_a like so to make my code more idiomatic:
----8<----
module Enumerable
def to_a(n = nil)
result = []
inclusion_condition = true
return result if n.to_i <= 0 and !block_given?
each do |*elements|
elements = elements.first if elements.size == 1
if block_given?
values = result.last
inclusion_condition = yield(*values) unless values.nil?
else
inclusion_condition = n != result.size
end
if inclusion_condition
result << elements
else
result.pop if block_given?
break result
end
end
result
end
end
----8<----
This allows, for example, the following:
Prime.new.to_a(10) # => [2, 3, 5, 7, 11, 13, 17, 19, 23, 29] , the first
10 primes
Prime.new.to_a {|prime| prime < 20} # => [2, 3, 5, 7, 11, 13, 17, 19] ,
all the primes under 20
Passed an integer paramater, the code will return an array that long, or
until the Enumerable runs out. Passed a block, it will return an array
of elements, adding elements until the block evaluates to false.
This code surely could use some hacking, refactoring, and possibly bug
fixing. I’ve made a post[1] on http://refactormycode.com just for that
purpose.
Thoughts?
[1]
http://refactormycode.com/codes/196-enumerable-to_a-with-terminating-conditions
-Ben Kudria
http://ben.kudria.net | Jabber: [email protected]
