ruby-core

Issue #13495 has been updated by marcandre (Marc-Andre Lafortune).

Status changed from Open to Rejected

`size` calculates the size lazily, without enumerating. If it can't, it returns `nil`.
`count` calculates the size by doing the actual enumeration. It never returns `nil`, but may never finish.

    (1..10**8).count # => takes a few seconds
    (1..10**8).size # => instant

Note that some ranges don't have sizes (mostly because I was too lazy to implement it for ranges of strings):

    ('a1'..'zz').size # => nil 
    ('a1'..'zz').count # => 259 

In short: understand the difference and use whichever method is right for the task.

----------------------------------------
Feature #13495: add Range#count as an alias to Range#size
https://bugs.ruby-lang.org/issues/13495#change-64459

* Author: AaronLasseigne (Aaron Lasseigne)
* Status: Rejected
* Priority: Normal
* Assignee: 
* Target version: 
----------------------------------------
For infinite ranges you can't call `count`, you have to call `size`.

~~~
irb> (1..Float::INFINITY).count # have to interrupt to stop it

irb> (1..Float::INFINITY).size
=> Infinity
~~~

The problem with this is that Range is an Enumerable. Enumerable does not have `size` it has `count`. So, if you want to implement a method for any Enumerable and you want to check the number of items you can't rely on `count`. Instead you have to do:

~~~
enum_count =
  begin
    size
  rescue NameError
    count
  end
~~~

Making Range#count as an alias of Range#size would allow people to make methods for Enumerable classes that rely on `count`.



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