Ruby: How to find out if a character is a letter or a digit?

Question

I just started tinkering with Ruby earlier this week and I've run into something that I don't quite know how to code. I'm converting a scanner that was written in Java into Ruby for a class assignment, and I've gotten down to this section:

if (Character.isLetter(lookAhead)) {           return id(); }  if (Character.isDigit(lookAhead)) {     return number(); } 

lookAhead is a single character picked out of the string (moving by one space each time it loops through) and these two methods determine if it is a character or a digit, returning the appropriate token type. I haven't been able to figure out a Ruby equivalent to Character.isLetter() and Character.isDigit().

Answer 1

Use a regular expression that matches letters & digits:

def letter?(lookAhead)   lookAhead.match?(/[[:alpha:]]/) end  def numeric?(lookAhead)   lookAhead.match?(/[[:digit:]]/) end 

These are called POSIX bracket expressions, and the advantage of them is that unicode characters under the given category will match. For example:

'ñ'.match?(/[A-Za-z]/)     #=> false 'ñ'.match?(/\w/)           #=> false 'ñ'.match?(/[[:alpha:]]/)  #=> true 

You can read more in Ruby’s docs for regular expressions.

Answer 2

The simplest way would be to use a Regular Expression:

def numeric?(lookAhead)   lookAhead =~ /[0-9]/ end  def letter?(lookAhead)   lookAhead =~ /[A-Za-z]/ end