Ruby

Bug #21780

Updated by zverok (Victor Shepelev) 2 days ago

In #21701 a new argument `size:` was introduced, and its default value is `nil` (unknown). 

 While I support the new argument, I'd argue that the default should be `Float::INFINITY`.  

 **Reasoning:** By _design_, `Enumerator.produce` is infinite (there is no internal condition to stop iteration), and the simplest, most straightforward usages of the method would produce _definitely infinite_ iterators, which the user than can limit with `take`, or `take_while` or similar methods. 

 To produce the enumerator that will stop by itself requires explicit raising of `StopIteration`, which I expect to be a (slightly) advanced technique, and those who use it might be more inclined to provide additional arguments to clarify the semantics. 

 While `Enumerator#size` is hardly frequently used now (other than in `#to_set`, which started the discussion), it might be in the future, and I believe it is better to stick with more user-friendly defaults. 

 Now: 
 ```ruby 
 # very trivial enumerator, but if you want it to have "proper" size, you need  
 # to not forget to use an elaborate argument and type additional 21 characters 
 Enumerator.produce(1, Enumerator.new(1, size: Float::INFINITY, &:succ) 

 # already non-trivial enumerator, which is hardly frequently used, but the  
 # current defaults correspond to its semantics: 
 Enumerator.produce(Date.today) Enumerator.new(Date.today) { 
   raise StopIteration if it.tuesday? && it.day.odd? 
   it + 1 
 } 
 ``` 

 With my proposal: 
 ```ruby 
 # trivial, most widespread case: 
 Enumerator.produce(1, Enumerator.new(1, &:succ).size #=> Infinity 

 # non-trivial case, with the enumerator designer clarifying their 
 # intention that "we are sure it stops somewhere": 
 Enumerator.produce(Date.today, Enumerator.new(Date.today, size: nil) { 
   raise StopIteration if it.tuesday? && it.day.odd? 
   it + 1 
 } 
 ```

Back