Commits on Jan 16, 2023

1. Implement DoubleEnded and ExactSize for Take<Repeat> and Take<RepeatW… …

   …ith>
   
   Repeat iterator always returns the same element and behaves the same way
   backwards and forwards.  Take iterator can trivially implement backwards
   iteration over Repeat inner iterator by simply doing forwards iteration.
   
   DoubleEndedIterator is not currently implemented for Take<Repeat<T>>
   because Repeat doesn’t implement ExactSizeIterator which is a required
   bound on DEI implementation for Take.
   
   Similarly, since Repeat is an infinite iterator which never stops, Take
   can trivially know how many elements it’s going to return.  This allows
   implementing ExactSizeIterator on Take<Repeat<T>>.
   
   While at it, observe that ExactSizeIterator can also be implemented for
   Take<RepeatWhile<F>> so add that implementation too.  Since in contrast
   to Repeat, RepeatWhile doesn’t guarante to always return the same value,
   DoubleEndedIterator isn’t implemented.
   
   Those changes render core::iter::repeat_n somewhat redundant.
   
   Issue: rust-lang#104434
   Issue: rust-lang#104729

   

   mina86 committed Jan 16, 2023
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