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Collections are a way for you to organize kata so that you can create your own training routines. Every collection you create is public and automatically sharable with other warriors. After you have added a few kata to a collection you and others can train on the kata contained within the collection.
Get started now by creating a new collection.
Char::to_lowercase()
andChar::to_uppercase()
return an iterator because Unicode supports special case-mappings where the lower- or uppercase version of a char can be multiple chars. But the kata input domain is plain ASCII which has a one-to-one case-mapping, so we just grab the first (and only) char produced by the iterator.why do you use next() ?