Implement tee for iterators

[BooleanCat]

Please provide a brief description of the change.

Support tee behaviour for iterators.

Which issue does this change relate to?

#88

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Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Comparison is base (b3ea617) 100.00% compared to head (eb938d2) 100.00%.

Additional details and impacted files

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  Coverage   100.00%   100.00%           
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  Files           24        26    +2     
  Lines          572       637   +65     
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+ Hits           572       637   +65     

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[BooleanCat]

@myusko This is a fairly naive implementation of tee. The buffer resizes make it fairly ineffeicient. I'd considered using a linked list instead but it's conceptually more difficult and will take more time for me to figure out.

What do you think about the API for this? I can change how it works under the hood to make it more efficient later but I'd curious about how easy it is to use.

[BooleanCat]

@williammartin I'd be curious too if you have any thoughts on how Tee is used here or better suggestions on making it more efficient than using a linked list or ring instead of a slice.

[BooleanCat]

I'd considered also using two buffered channels but I'd need the channels to be unbounded in size in order to not lock Next from iterators where one is far ahead of the other.

[BooleanCat]

On the usage suggestion - an alternative would be to have Tee directly return the two iterators:

one, two := iter.Count().Take(3).Tee()

I could then make TeeIters private - it's never intended for direct use anyway.

e.g. https://github.com/BooleanCat/go-functional/commit/b8fad8b44a4acaaa4dba52f478f50311a35821c5