Empty Variables

  • published on September 23rd, 2008

    One of the more confusing differences between Ruby and PHP is the different way in which the languages treat empty variables when evaluating statements.

    The chart below shows the most common scenarios you may encounter. We have several similar charts in the Rails for PHP Developers book with other handy information.

    PHP if ($x) empty($x)  
    $x = ""; FALSE TRUE  
    $x = null; FALSE TRUE  
    $x = array(); FALSE TRUE  
    $x = false; FALSE TRUE  
    $x = 0; FALSE TRUE  
    $x = "0"; FALSE TRUE  
     
    Ruby if (x) x.empty? x.blank?**
    x = "" TRUE TRUE TRUE
    x = nil FALSE u/m * TRUE
    x = [] TRUE TRUE TRUE
    x = {} TRUE TRUE TRUE
    x = false FALSE u/m * TRUE
    x = 0 TRUE u/m * FALSE
    x = "0" TRUE FALSE FALSE
    * NoMethodError: undefined method ** Only Available in Rails

    While PHP evaluates all empty variable as false, Ruby only evaluates nil and false to be false. Some Ruby objects have an empty? method, but this is not always as useful as you might expect. The method is only available on some objects, and calling nil.empty? or false.empty? will result in NoMethodError.

    The Rails framework adds a consistent method named blank? that exists on all objects as a single way to check if a variable contains a blank object. Rails has also very recently added a corresponding present? method, which is equivalent of !blank?

    Handling Zero

    Handling zero values often trips up beginning Ruby programmers. This cause of this confusion is best demonstrated by the following two code snippets.

    PHP

    $num = 0;
if ($num) {
  // This not evaluated.
}

    Ruby

    num = 0
if num
  # This is evaluated!
end

    Refer to the chart above as you read the snippets. While this may seem counter intuitive coming from PHP, for the most part it’s not a problem.

    In Ruby code, we typically know when we’re working with numbers, or we can cast to them. We can then simply do something like these examples:

    Ruby

    num = User.count
 
if num > 0
  puts "there are some users"
end
 
if num.zero?
  puts "no users here"
end

    Similarly, it is important to note that zero (0 and "0") evaluates to true using 0.blank?.

This entry was posted on Tuesday, September 23rd, 2008 at 4:19 pm. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.

2 comments

  • comment by lowell 24 Sep 08

    “Similarly, it is important to note that zero (0 and “0″) evaluates to true using 0.blank?.”

    of course.. in ruby, everything but nil and false itself is true.

  • comment by Custom PHP 12 Nov 08

    Might mess someone up if they are going back and forth or working on PHP apps while working on Ruby apps.

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