Language-Portable Example Programs

Question

At the moment I am learning Objective-C 2. I'm aware that it's used heavily by Mac developers, but I'm more interested in learning the language at this point in time than the frameworks for developing on Mac OS X/iPhone (except for Foundation). In order to do this I want to write a few intermediate* console applications, but I'm stuck for ideas.

Most examples are something along the lines of "Write a Fraction class that has getters/setters and a print function", which isn't very challenging coming from a C++ background. I'd like some generic examples of programs, but I don't want them to include any Objective-C implementation details. I want to figure out the program structure/write my own interfaces and learn the language from there.

In summary: I am curious as to what example programs Objective-C programmers would recommend for exploring the language.

An example of an "intermediate" application would be something along the lines of "Write a program that takes a URL from the command line and returns the number of occurrences of a certain word in data returned:

example -url www.google.com -word search

Answer 1

"Project Euler" is a standard response for this kind of thing, but I get the feeling that you're less interested in being told to implement algorithmic stuff (since that knowledge is easier to port between languages) and more interested in miniprojects that will familiarize you with core libraries. Is this fair?

If so, IMO, you ought to know the basics of how to do the following with the standard libraries of language you hope to use for serious work:

1. Standard IO
2. Network IO
3. Disk IO and navigating the filesystem
4. Regexp utilities
5. Structured data (XML libraries and CSV libraries if they exist)

Programming problems I would recommend for those:

1. It sounds like you've already done this.
2. A very simple proxy - something like what you described in your post, but that listens on a port for a message containing a URL rather than taking it on the command line, and likewise returns the results to whatever contacted it over the network rather than outputting to stdio. [Obviously you need to have the machine behind an appropriate firewall for this!]
3. Something which takes a directory path and recursively tallies the number of lines its children contain. (So, get the directory's listing, open each child file and count the number of line breaks. Then open each of its child directories, get their listings, ...) Record any errors encountered (e.g., no read privileges) in a reasonable way. Write out the final results to file in the directory supplied.
4. Usually if I tool around in a language enough, I'll run across some problem which I just naturally find myself using regexps for. I'll assume the same is true for you and punt this element for now.
5. Fetch StackOverflow.com, and [by putting it into a DOM model and navigating that] determine whether this question is still on the front page.

Answer 2

I got the most out of Objective-C by exploring it with a testing framework. I have written a short blog post about it. You should also wrap your head around the memory management conventions employed by Objective-C, reference counting takes a little time to get used to but works very well if responsibilities are clearly segregated (I have written about that on my blog too).

By getting my hands dirty on a testing framework (GHUnit for that matter), I was able to learn far more about the language than I could have in a "traditional" way. Of course you'll need a little pet project, otherwise this approach doesn't make sense.

I don't think your example is a very good idea as it requires you to mess with http connections, resources etc. which is a little framework specific after all. Parsing a text file would be a little easier in this regard. Using a unit testing framework has the following advantages for you:

• learn about platform specific build systems and deployment details
• forced to develop components in a loosely coupled fashion from the ground up
• thereby exploring unique mechanisms of the language, that might require new or make known patterns redundant (e.g. categories make dependency injection obsolete etc.)
• fast compile-test cycle, less time spent in front of the debugger
• combined with source control: painless experiments

You should also look into the testing framework implementation, as testing frameworks always require to work with metadata to some extend. Testing frameworks are often used together with isolation frameworks. They basically create objects at runtime that comply to certain interfaces and act as stand-ins for concrete objects. Looking at their implementation will teach you about the runtime manipulations that can be done in Objective-C (keyword: Method-Swizzling)