[ruby-core:98153] [Ruby master Feature#16833] Add Enumerator#empty?

Issue #16833 has been updated by marcandre (Marc-Andre Lafortune).


Enumerators can behave very differently than arrays. Some have side-effects. What's supposed to happen with those?

```
require 'stringio'
s = StringIO.new("first\nsecond\nthird\nlast").each_line
s.first # => "first"
s.first # => "second"
s.empty? # => false
s.first # => "third" or "last"?
s.empty? # => false or true?
```

You may want to rethink your algorithm, or simply call `to_a` once and act on the array.

For similar reasons, `Enumerator#size` exist and is lazy, but it may return `nil` (e.g. `s.size` above) so wouldn't completely serve your purpose either.

For these reason I think you should either close your request or elaborate on an actual use case where a generic enumerator is being used, as well as the actual effect of `empty?` on external iterators, ...


----------------------------------------
Feature #16833: Add Enumerator#empty?
https://bugs.ruby-lang.org/issues/16833#change-85393

* Author: f3ndot (Justin Bull)
* Status: Open
* Priority: Normal
----------------------------------------
It was surprising to me that Enumerator, something mixed into Array, does not include `#empty?`. I think it is reasonable to assume people may have to guard iterating and other logic based on the emptiness of an enumerator, such was my case.


``` ruby
 # pretend there's convoluted enumerator logic to produce this structure
table_rows = [{ data: ['First', 'Second', 'Third'], config: {} }, { data: [4, 5, 6], config: { color: 'red' } }].to_enum

return if table_rows.empty?

table_header = table_rows.first[:data] # requires an empty guard
# ...
```

I propose that it simply behaves as `#take(1).to_a.empty?` instead of aliasing to something like `#none?` because of falsey elements or `#size == 0` because of potential `nil` returns:

```ruby
[].to_enum.empty?        # => true
[false].to_enum.empty?   # => false
[nil].to_enum.empty?     # => false
[0].to_enum.empty?       # => false
[1, 2, 3].to_enum.empty? # => false
```

---Files--------------------------------
add-enumerable-empty.patch (1.99 KB)


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