Add section about Enumerable#lazy

Author: ydakuka

README.adoc

@@ -4954,6 +4954,31 @@ LOREM
 "when an unknown printer took a galley of type and scrambled it to make a type specimen book."
 ----
 
+== Enumerable
+
+=== Leverage `#lazy` to Optimize Memory Usage [[leverage-lazy-to-optimize-memory-usage]]
+
+Using `Enumerable#lazy` in combination with methods like `Enumerable#first` or `Enumerable#take` can be very efficient, especially for operations on large collections, datasets and infinite sequences seamlessly.
+
+Enumerator::Lazy can be constructed from any Enumerable with the `Enumerable#lazy` method without evaluating them immediately, and evaluating values on as-needed basis.
+
+The real enumeration is performed when any non-redefined Enumerable method is called.
+
+[source,ruby]
+----
+# bad
+(0..).uniq { |x| x + 2 }.first(10)
+(0..10000000).select { |x| x + 2 }.take(10)
+
+# good
+(0..).lazy.uniq { |x| x + 2 }.first(10)
+(0..10000000).lazy.select { |x| x + 2 }.take(10)
+----
+
+=== Convert Lazy Enumerator to a Normal Enumerator with `#eager` [[convert-lazy-enumerator-to-a-normal-enumerator-with-eager]]
+
+`Enumerable#eager` converts a lazy enumerator back to a non-lazy Normal Enumerator for compatibility with methods that expect standard enumerable object.
+
 == Heredocs
 
 === Squiggly Heredocs [[squiggly-heredocs]]