Тимофей Даньшин wrote:
Is it a good idea to split all those classes into categories for
writing, reading and testing? For example, Database (Writing),
Database(Reading), Database(Testing) and so on? Or is it a silly
thing to do for some reason?
I suggest reading about why Objective-C has categories. Here's one
simple description. You can probably google others.
http://en.wikipedia.org/wiki/Objective-C#Categories
To me, the real question to ask isn't "Should I use categories?", it
should be "What categories should I use?". That is, what does your
most basic class represent ("Database" might be too large a concept
to represent well), and what functionality resides in that most basic
representation? Then what are the related groups of functionality
that are added to that basic representation? Then which of those are
best done as categories, which as subclasses, and which as formal
protocols?
If you're asking "Should I use categories?", then it seems likely the
problem hasn't been broken down far enough yet. Once that breaking
down occurs, then classes, protocols, and categories will tend to
become apparent as a natural consequence of how you break the problem
down in order to reach a desired solution. Breaking problems down,
and doing it well, can be the hardest part of reaching a solution.
Elaborating a little on the parenthetical ("Database" might be too
large a concept to represent well), consider how Java works with SQL
databases. It has the JDBC classes and interfaces, and there isn't a
"Database" class anywhere among them. Instead, there are
Connection's, various Metadata's, Statement's, and ResultSets. All
are abstract interfaces (equivalent to Obj-C formal protocol). The
concept of "a database" is only implied, in that a Connection to "a
database" is created from a URL and other things, and is supported by
a Driver for the DBMS product being connected to.
This is not meant to suggest JDBC is the best or only way to create a
database interface. It's just to illustrate that creating a class
Database and a category Reading, which don't naturally emerge from
breaking the problem down, could be a poor way to solve the problem.
-- GG
Subject: Categories and splitting an app into logical blocks.
From: Тимофей Даньшин <em...@hidden>
Date: Fri, 15 May 2009 23:57:07 +0400
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Hello.
Suppose, I have an app that, for example, works with a database. It
can write to the db, it can select things. There is a class that
works with the database, a class that controls that class and a class
that interacts with the gui. And, of course, there is some testing
code in all the three "layers".
Is it a good idea to split all those classes into categories for
writing, reading and testing? For example, Database (Writing),
Database(Reading), Database(Testing) and so on? Or is it a silly
thing to do for some reason?
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