Improve Enumerator.produce docs

* Add to NEWS;
* Add examples of while-alike cycles with practical tasks.

2 files changed, 22 insertions, 0 deletions

diff --git a/NEWS b/NEWS
index 5379caa740..acc3d0c719 100644
--- a/NEWS
+++ b/NEWS
@@ -248,6 +248,13 @@ Enumerator::
 
   New methods::
 
+    * Added Enumerator.produce to generate Enumerator from any custom
+      data-transformation.  [Feature #14781]
+
+        require 'date'
+        dates = Enumerator.produce(Date.today, &:succ) #=> infinite sequence of dates
+        dates.detect(&:tuesday?) #=> next tuesday
+
     * Added Enumerator::Lazy#eager that generates a non-lazy enumerator
       from a lazy enumerator.  [Feature #15901]
 
diff --git a/enumerator.c b/enumerator.c
index eee3a34e6b..06e2a9e6a7 100644
--- a/enumerator.c
+++ b/enumerator.c
@@ -2923,6 +2923,21 @@ producer_size(VALUE obj, VALUE args, VALUE eobj)
  *
  *   ancestors = Enumerator.produce(node) { |prev| node = prev.parent or raise StopIteration }
  *   enclosing_section = ancestors.find { |n| n.type == :section }
+ *
+ * Using ::produce together with Enumerable methods like Enumerable#detect,
+ * Enumerable#slice, Enumerable#take_while can provide Enumerator-based alternative
+ * for +while+ and +until+ cycles:
+ *
+ *   # Find next Tuesday
+ *   require 'date'
+ *   Enumerator.produce(Date.today, &:succ).detect(&:tuesday?)
+ *
+ *   # Simple lexer:
+ *   require 'strscan'
+ *   scanner = StringScanner.new('7+38/6')
+ *   PATTERN = %r{\d+|[-/+*]}
+ *   p Enumerator.produce { scanner.scan(PATTERN) }.slice_after { scanner.eos? }.first
+ *   # => ["7", "+", "38", "/", "6"]
  */
 static VALUE
 enumerator_s_produce(int argc, VALUE *argv, VALUE klass)