From: Yui NARUSE <naruse@...>
Date: 2011-09-28T07:38:02+09:00
Subject: [ruby-core:39753] [Ruby 1.9 - Feature #5372] Promote blank? to a core protocol


Issue #5372 has been updated by Yui NARUSE.


This seems the long discussed question, what is a zero element.
But I don't think this proposal is not worth breaking ActiveSupport's blank?.

Anyway what is the usecase of this?
I doubt a closed io is a zero element.
Do you have a case that you are happy if it is a zero element.
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Feature #5372: Promote blank? to a core protocol
http://redmine.ruby-lang.org/issues/5372

Author: Alex Young
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 1.9.4


I don't think there's been a project I've used that hasn't made use of this pattern:

  if thing.nil? || thing.empty?

somewhere in its source.  This is necessary because it is idiomatic to return nil where other languages might return a null object, and there is no universal test for nullity which a user-implemented class can provide without issues.

Facets (and ActiveSupport) define a #blank? protocol which allows for the above to be replaced with:

  if thing.blank?

Being able to type this on a first iteration saves forgetting one of the cases and having to come back to fix a bug later.  For projects where I cannot directly use Facets or ActiveSupport, I always find that I rewrite a version for myself.  It would be very convenient not to have to do this every time, and this is clearly a common case, so I propose that #blank? be implemented on the following classes:

  Object: to return false
  String: aliased to #empty?
  NilClass: to return true
  TrueClass: to return false
  FalseClass: to return true
  Array: aliased to #empty?
  Hash: aliased to #empty?
  Fiber: to return !alive?
  Numeric: aliased to #zero?
  IO: aliased to #closed?
  MatchData: to return #to_s.blank?
  Process::Status: aliased to #exited?
  Range: to return self.include?(self.begin)
  Struct: subclass instances to return values.blank?
  Thread: to return !alive?
  ThreadGroup: to return list.blank?

Some of these uses aren't described by the word "blank?" very well (and ActiveSupport's String#blank? is somewhat different), so as a sub-feature I'd like to suggest "null?" as an alternative method name.

Apologies if this has been proposed and rejected before, but a quick search of redmine didn't show anything relevant.


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