NilClaass#blank? is incredibly useful because it compliments String#blank? and Array#blank?, which are mostly[1] an alias of #empty?. For most uses where you al

NilClaass#blank? is incredibly useful because it compliments String#blank? and Array#blank?, which are mostly[1] an alias of #empty?. For most uses where you already know you have a string or array, you probably want to use #empty? directly. The entire point behind #blank? is that it provides a cross-class[2] method that works even when the object doesn't exist (and you get nil instead). This was designed for Rails to simplify situations such as the params[3] (parsed URL query string), which might not have a particular value. # when handling "/action?foo=bar" params[:foo] # => "bar" # when handling "/action?foo=" params[:foo] # => "" # when handling "/action" params[:foo] # => nil With #blank?, you only need one function call to handle both the empty string and nil cases. if params[:foo].blank? # render a static placeholder (never looks at params) else # render Foo's markup, using the value in params[:foo] end If you cared about the empty states other than as a generic "it's blank", other methods may be more appropriate. > why does FalseClass respond to blank? with `true`, but not TrueClass That's a good question. I would have assumed both true and false as not-blank (#blank? => false), as those could both be entered (#present?) values. I suspect it's related to HTML forms only including successful controls[4] in the query string. [1] https://github.com/rails/docrails/blob/master/activesupport/lib/active_support/core_ext/object/blank.rb#L100 https://github.com/rails/docrails/blob/master/activesupport/... [2] see: duck-typing [3] http://api.rubyonrails.org/classes/ActionController/Parameters.html http://api.rubyonrails.org/classes/ActionController/Paramete... [4] http://www.w3.org/TR/html401/interact/forms.html#h-17.13.3.2 http://www.w3.org/TR/html401/interact/forms.html#h-17.13.3.2