Issue #10498 has been updated by Franck Verrot.


Robert Klemme wrote:
> > [...] I wasn't able to find a way to fine-tune this based on the block's arity as mentioned previously.
> 
> That seems fairly easy:
> 
> ~~~
> def lp(&b)
>   return to_enum(:lp) unless b
>   
>   if b.arity == 0
>     while true
>       b[]
>     end
>   else
>     i = 0
> 
>     while true
>       b[i]
>       i += 1
>     end
>   end
> 
>   raise "This must never happen"
> end
> ~~~

I meant in C but yes, given we could have `Kernel#loop_with_index` implemented in Ruby, it would be a no-brainer.

> > On the other hand, you'd need 4,611,686,018,427,387,903 iterations before paying the price of using `BigNum`s, which compared to the code you're having in the block would probably be more expensive than incrementing a `BigNum`.
> 
> Yes, but as a user of loop you would not have a choice any more.  I'd rather use the approach from above or define another method loop_with_index or use the approach with Generator and a constant.  I would definitively not unconditionally provide a counter.

I get your point.

`times` does yield a counter, would you say it's the same concern?



----------------------------------------
Feature #10498: Make `loop` yield a counter
https://bugs.ruby-lang.org/issues/10498#change-50003

* Author: Franck Verrot
* Status: Open
* Priority: Normal
* Assignee: ruby-core
* Category: core
* Target version: current: 2.2.0
----------------------------------------
# Problem

Teaching Ruby, we always end up with that type of construct

```ruby
i = 0
loop do
  i += 1
  # do something with i....
  raise StopIteration if i ...
end
```

# Solution

What I propose with this patch is making `loop` yield the iteration count:

```ruby
loop do |i|
  # do something with i....
  raise StopIteration if i ...
end
```

`i` starts at 0 and stops at `FIXNUM_MAX` (there's no `Float::Infinity` equivalent for integers).

# Alternate solution

`Integer#times` could work if we had an `<Integer's infinity>` object, so we would just do `<Integer's Infinity>.times { |i| ... }`.

Also, this is the very first patch I submit to Ruby, I might have done something horrible, feel free to tell me :-)

---Files--------------------------------
0001-vm_eval.c-loop-now-yields-a-incremented-counter.patch (1.74 KB)
0001-vm_eval.c-loop-now-yields-a-incremented-counter.patch (1.86 KB)


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