Documentation of Regex.new

[drosehn]

The documentation for Regex.new at Regex.html has the line:

Regex.new("^a-z+:\s+\w+")                     # => /^a-z+:\s+\w+/

As does the source code for Regex.initialize in src/regex.cr

That is not correct, because the parsing of string values is not the same as the parsing of Regex values, particularly when it comes to escaped characters like \d.

dumb_rx = Regex.new( "\s+\d+\s+" )
if "aa 22 cc" =~ dumb_rx
  printf "single-slash Match\n"
else
  printf "single-slash No Match\n"
end

dumb_rx = Regex.new( "\\s+\\d+\\s+" )
if "aa 22 cc" =~ dumb_rx
  printf "double-slash Match\n"
else
  printf "double-slash No Match\n"
end

produces:

single-slash No Match
double-slash Match

(which is what I would expect it to do, of course).

[drosehn]

Also, in Ruby one can use a regexp-value as the first parameter to Regexp.new(), to avoid the extra level of escaping that you'd need when using a string-value for that parameter. Crystal does not allow that, although I do not know if that was intentional. If the user tries:

dumb_rx = Regex.new( /\s+\d+\s+/ )
if "aa 22 cc" =~ dumb_rx
  printf "single-slash Match\n"
else
  printf "single-slash No Match\n"
end

they get the compile-time error of:

Error in line 1: instantiating 'Regex:Class#new(Regex)'

instantiating 'Regex#initialize(Regex)'

in /usr/lib/crystal/regex.cr:224: undefined method 'gsub' for Regex

    source = source.gsub('\u{0}', "\\0")
                    ^~~~

================================================================================

Regex trace:

  /usr/lib/crystal/regex.cr:222

      def initialize(source, @options : Options = Options::None)

You might wonder why anyone would bother doing Regexp.new( /patrn/ ) instead of simply using /patrn/, and I must admit I do not know why I started doing that. Maybe it had something to do with the state of ruby back in 2002. But if crystal does intend to not allow that, then maybe the definition for Regex.initialize should be:

def initialize(source : String, @options : Options = Options::None)

instead of:

def initialize(source, @options : Options = Options::None)

?