Ruby Enumerable extension. Main idea is lazy computations within enumerators.

Install as a gem:

sudo gem install deferred_enum

This gem introduces DeferredEnumerator class:

ary = [1, 2, 3, 4]
deferred = ary.defer                 # #<DeferredEnumerator: [1, 2, 3, 4]:each>

DeferredEnumerator brings some optimizations to all?, any? and none? predicates

deferred.all?(&:even?)               # Will stop iteration after first false-result = 1 iteration
deferred.none?(&:even?)              # 2 iterations
deferred.any?(&:even?)               # 2 iterations

It also introduces lazy versions of Enumerable’s #select, #map and #reject methods

deferred.map { |i| i + 1 }           # #<DeferredEnumerator: #<Enumerator::Generator>:each>
deferred.select { |i| i.even? }      # #<DeferredEnumerator: #<Enumerator::Generator>:each>
deferred.reject { |i| i.odd? }       # #<DeferredEnumerator: #<Enumerator::Generator>:each>

So you can safely chain your filters, they won’t be treated as arrays:

deferred.map(&:succ).select(&:even?) # #<DeferredEnumerator: #<Enumerator::Generator>:each>

You can build chains of Enumerables:

deferred.concat([2]).to_a            # [1, 2, 3, 4, 2]

Or append elements to the end of enumerator:

deferred << 2

You can even remove duplicates from enumerator, though this operation can be tough:

deferred.uniq                        # #<DeferredEnumerator: #<Enumerator::Generator>:each>

There are many other methods in DeferredEnumerator, please refer to documentation.