Posts in this category
- Current State of Exceptions in Rakudo and Perl 6
- Meet DBIish, a Perl 6 Database Interface
- doc.perl6.org and p6doc
- Exceptions Grant Report for May 2012
- Exceptions Grant Report -- Final update
- Perl 6 Hackathon in Oslo: Be Prepared!
- Localization for Exception Messages
- News in the Rakudo 2012.05 release
- News in the Rakudo 2012.06 release
- Perl 6 Hackathon in Oslo: Report From The First Day
- Perl 6 Hackathon in Oslo: Report From The Second Day
- Quo Vadis Perl?
- Rakudo Hack: Dynamic Export Lists
- SQLite support for DBIish
- Stop The Rewrites!
- Upcoming Perl 6 Hackathon in Oslo, Norway
- Pattern Matching and Unpacking
- Rakudo's Abstract Syntax Tree
- The REPL trick
- A shiny perl6.org site
- Creating an entry point for newcomers
- An offer for software developers: free IRC logging
- Announcing try.rakudo.org, an interactive Perl 6 shell in your browser
- Another perl6.org iteration
- Blackjack and Perl 6
- Why I commit Crud to the Perl 6 Test Suite
- This Week's Contribution to Perl 6 Week 5: Implement Str.trans
- This Week's Contribution to Perl 6
- This Week's Contribution to Perl 6 Week 8: Implement $*ARGFILES for Rakudo
- This Week's Contribution to Perl 6 Week 6: Improve Book markup
- This Week's Contribution to Perl 6 Week 2: Fix up a test
- This Week's Contribution to Perl 6 Week 9: Implement Hash.pick for Rakudo
- This Week's Contribution to Perl 6 Week 11: Improve an error message for Hyper Operators
- This Week's Contribution to Perl 6 - Lottery Intermission
- This Week's Contribution to Perl 6 Week 3: Write supporting code for the MAIN sub
- This Week's Contribution to Perl 6 Week 1: A website for proto
- This Week's Contribution to Perl 6 Week 4: Implement :samecase for .subst
- This Week's Contribution to Perl 6 Week 10: Implement samespace for Rakudo
- This Week's Contribution to Perl 6 Week 7: Implement try.rakudo.org
- What is the "Cool" class in Perl 6?
- Report from the Perl 6 Hackathon in Copenhagen
- Custom operators in Rakudo
- A Perl 6 Date Module
- Defined Behaviour with Undefined Values
- Dissecting the "Starry obfu"
- The case for distributed version control systems
- Perl 6: Failing Softly with Unthrown Exceptions
- Perl 6 Compiler Feature Matrix
- The first Perl 6 module on CPAN
- A Foray into Perl 5 land
- Gabor: Keep going
- First Grant Report: Structured Error Messages
- Second Grant Report: Structured Error Messages
- Third Grant Report: Structured Error Messages
- Fourth Grant Report: Structured Error Messages
- Google Summer of Code Mentor Recap
- How core is core?
- How fast is Rakudo's "nom" branch?
- Building a Huffman Tree With Rakudo
- Immutable Sigils and Context
- Is Perl 6 really Perl?
- Mini-Challenge: Write Your Prisoner's Dilemma Strategy
- Longest Palindrome by Regex
- Perl 6: Lost in Wonderland
- Lots of momentum in the Perl 6 community
- Monetize Perl 6?
- Musings on Rakudo's spectest chart
- My first executable from Perl 6
- My first YAPC - YAPC::EU 2010 in Pisa
- Trying to implement new operators - failed
- Programming Languages Are Not Zero Sum
- Perl 6 notes from February 2011
- Notes from the YAPC::EU 2010 Rakudo hackathon
- Let's build an object
- Perl 6 is optimized for fun
- How to get a parse tree for a Perl 6 Program
- Pascal's Triangle in Perl 6
- Perl 6 in 2009
- Perl 6 in 2010
- Perl 6 in 2011 - A Retrospection
- Perl 6 ticket life cycle
- The Perl Survey and Perl 6
- The Perl 6 Advent Calendar
- Perl 6 Questions on Perlmonks
- Physical modeling with Math::Model and Perl 6
- How to Plot a Segment of a Circle with SVG
- Results from the Prisoner's Dilemma Challenge
- Protected Attributes Make No Sense
- Publicity for Perl 6
- PVC - Perl 6 Vocabulary Coach
- Fixing Rakudo Memory Leaks
- Rakudo architectural overview
- Rakudo Rocks
- Rakudo "star" announced
- My personal "I want a PONIE" wish list for Rakudo Star
- Rakudo's rough edges
- Rats and other pets
- The Real World Strikes Back - or why you shouldn't forbid stuff just because you think it's wrong
- Releasing Rakudo made easy
- Set Phasers to Stun!
- Starry Perl 6 obfu
- Recent Perl 6 Developments August 2008
- The State of Regex Modifiers in Rakudo
- Strings and Buffers
- Subroutines vs. Methods - Differences and Commonalities
- A SVG plotting adventure
- A Syntax Highlighter for Perl 6
- Test Suite Reorganization: How to move tests
- The Happiness of Design Convergence
- Thoughts on masak's Perl 6 Coding Contest
- The Three-Fold Function of the Smart Match Operator
- Perl 6 Tidings from September and October 2008
- Perl 6 Tidings for November 2008
- Perl 6 Tidings from December 2008
- Perl 6 Tidings from January 2009
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- Perl 6 Tidings from April 2009
- Perl 6 Tidings from May 2009
- Perl 6 Tidings from May 2009 (second iteration)
- Perl 6 Tidings from June 2009
- Perl 6 Tidings from August 2009
- Perl 6 Tidings from October 2009
- Timeline for a syntax change in Perl 6
- Visualizing match trees
- Want to write shiny SVG graphics with Perl 6? Port Scruffy!
- We write a Perl 6 book for you
- When we reach 100% we did something wrong
- Where Rakudo Lives Now
- Why Rakudo needs NQP
- Why was the Perl 6 Advent Calendar such a Success?
- What you can write in Perl 6 today
- Why you don't need the Y combinator in Perl 6
- You are good enough!
Thu, 09 Sep 2010
Protected Attributes Make No Sense
In C++, you can declare an attribute or a method as "protected". Which means that it is private, but subclasses can still access them.
This makes just as much sense as saying you only get access to these attributes if you wear a funny yellow hat.
I'll try to explain why.
Encapsulation has the advantage that you can change the implementation of a class without changing the API. If you write a library, that means you don't break your user's code if you change some internals.
However your users can not only instantiate your classes, but they can also inherit from them. Which means they can put a funny yellow hat on. There is no restriction as to who can inherit from your classes. Which makes protected attributes part of the public interface.
So, if you want to change the implementation of a class, you can't change how a protected attribute or method works, and what data it stores. If you do, you break all subclasses. Which not only exist in your own source tree, but in your user's source tree too. If you think that changing the implementation will also change protected attributes or methods, make them private.
So if protected methods are essentially part of the public API anyway, why not declare them as public? Why require your user to wear a funny yellow hat (aka declare an inheritance relation) while using your class? There is no good reason.
When seasoned C++ programmers hear that, they often respond with "but if I declare my private data as private a subclass doesn't have access to it! How can it work properly?". The answer is simple: You must provide a sufficiently powerful public API. Your users will be grateful.
One more thing: people often come up with an analogy to the real world, and claim that your kids also have access to your house or flat. This analogy is broken, because in the real world the parents have to take actions to get children (or give somebody the same status as your children). In the programming world, every outsider can write a child class of your classes.
(The reason I posted this in the Perl 6 section of this blog is that Perl 6 has no protected attributes. Which has spawned many interesting discussions, which were the precursor to this blog post.)
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