Add Enumerable#lazy guideline to "Collections" section

README.adoc

@@ -4915,6 +4915,25 @@ Predicate methods without arguments can't replace `count` expressions when colle
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+=== 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 - instantiates the entire collection into memory first
+(0..).uniq { |x| x + 2 }.first(10)
+(0..10000000).select { |x| x % 1000 }.first(5)
+
+# good - evaluates elements on an as-needed basis
+(0..).lazy.uniq { |x| x + 2 }.first(10)
+(0..10000000).lazy.select { |x| x % 1000 }.first(5)
+----
+
 == Numbers
 
 === Underscores in Numerics [[underscores-in-numerics]]