Re: If design patterns are not supposed to produce reusable code then why use them?

Richard Quadling wrote:

2009/12/30 Tony Marston <tony@marston-home.demon.co.uk>:

I have recently been engaged in an argument via email with someone who criticises my low opinion of design patterns (refer to http://www.tonymarston.net/php-mysql/design-patterns.html ). He says that design patterns are merely a convention and not a reusable component. My argument is that something called a pattern is supposed to have a recurring theme, some element of reusability,

Design patterns re-use the approach to solving a particular problem set. Note that I said approach, because the code may not be re-usable, but the tenets of the solution are embodied by the pattern regardless of the language used. In this way, design patterns are indeed re-usable. When you see that a particular problem falls within the domain of a Design Pattern, then the implementation is straightforward since you can use the design pattern to guide your implementation.

so that all subsequent implementations of a pattern should require less effort than the first implementation. If design patterns do not provide any reusable code then what is the point of using them?

Each subsequent use of a design pattern should indeed require less effort. As you absorb fully the pattern, it becomes easier and easier to see how problems fit within one pattern or another or multiple patterns. Having at that point already implemented solutions using design patterns, it should become easier each time you create a solution using a previously used design pattern.

I do not use design patterns as I consider them to be the wrong level of abstraction. I am in the business of designing and developing entire applications which comprise of numerous application transactions, so I much prefer to use transaction patterns (refer to http://www.tonymarston.net/php-mysql/design-patterns-are-dead.html and http://www.tonymarston.net/php-mysql/transaction-patterns.html ) as these provide large amounts of reusable code and are therefore a significant aid to programmer productivity. What is your opinion? Are design patterns supposed to provide reusable code or not? If not, and each implementation of a pattern takes just as much time as the first, then where are the productivity gains from using design patterns?

If I ask you to classify bugs by genus, does it not become easier and easier to classify any given bug based on your previous experience of knowing what constitutes membership in a particular genus? The same is true of design patterns. Cheers, Rob. -- http://www.interjinn.com Application and Templating Framework for PHP