[ruby-core:84559] [Ruby trunk Feature#13890] Allow a regexp as an argument to 'count', to count more interesting things than single characters

Issue #13890 has been updated by duerst (Martin D端rst).


Python allows to count strings, as follows:

`str.count(sub[, start[, end]])`
Return the number of non-overlapping occurrences of `substring` `sub` in the range `[start, end]`. Optional arguments `start` and `end` are interpreted as in slice notation.

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Feature #13890: Allow a regexp as an argument to 'count', to count more interesting things than single characters
https://bugs.ruby-lang.org/issues/13890#change-69097

* Author: duerst (Martin D端rst)
* Status: Open
* Priority: Normal
* Assignee: 
* Target version: 
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Currently, String#count only accepts strings, and counts all the characters in the string.

However, I have repeatedly met the situation where I wanted to count more interesting things in strings.
These 'interesting things' can easily be expressed with regular expressions.

Here is a quick-and-dirty Ruby-level implementation:

````Ruby
class String
  alias old_count count

  def count (what)
    case what
    when String
      old_count what
    when Regexp
      pos = -1
      count = 0
      count += 1 while pos = index(what, pos+1)
      count
    end
  end
end
````

Please note that the implementation counts overlapping occurrences; maybe there is room for an option like `overlap: :no`.



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