Feature #16441
Updated by sawa (Tsuyoshi Sawada) over 4 years ago
The method is just like `#take_while`, but also includes the item where condition became true. Examples of usefulness: ```ruby str = <<DOC prologue << 1 2 3 >> epilogue DOC ``` # Imagine we want to take everything starting from `<<` << to `>>` >> in short and clean Ruby. Ruby # Surprisingly, our best guess would be infamous flip-flop: ```ruby p str.each_line(chomp: true).filter_map { _1 if _1 == '<<'.._1 == '>>' } # => ["<<", "1", "2", "3", ">>"] ``` # Trying to achieve this with `Enumerator`, Enumerator, you _almost_ can express it, but the last line is lost: ```ruby but... p str.each_line(chomp: true).drop_while { _1 != '<<' }.take_while { _1 != '>>' } # => ["<<", "1", "2", "3"] ``` -- the last line is lost. # So, Enumerable leaves us with this (which is harder to read, due to additional `.first`): ```ruby p str.each_line(chomp: true).drop_while { _1 != '<<' }.slice_after { _1 == '>>' }.first # => ["<<", "1", "2", "3", ">>"] ``` # With proposed method: ```ruby p str.each_line(chomp: true).drop_while { _1 != '<<' }.take_while_after { _1 != '>>' } # => ["<<", "1", "2", "3", ">>"] ``` The idea is the same as with flip-flops `..` vs `...` (sometimes we need to include the last element matching the condition, sometimes don't), and `while ... end` vs `do ... while`. Another example (from `Enumerator.produce` [proposal](https://bugs.ruby-lang.org/issues/14781)): ```ruby require 'strscan' scanner = StringScanner.new('7+38/6') p Enumerator.produce { scanner.scan(%r{\d+|[-+*/]}) }.take_while { !scanner.eos? } # expresses meaning, but loses last element # => ["7", "+", "38", "/"] p Enumerator.generate { scanner.scan(%r{\d+|[-+*/]}) }.slice_after { scanner.eos? }.first # slice_after {}.first again # => ["7", "+", "38", "/", "6"] p Enumerator.produce { scanner.scan(%r{\d+|[-+*/]}) }.take_while_after { !scanner.eos? } # => ["7", "+", "38", "/", "6"] ``` PS: Not sure about the name, suggestions are welcome