TweetFollow Us on Twitter

Apr 97 Getting Started

Volume Number: 13 (1997)
Issue Number: 4
Column Tag: Getting Started

A First Look at Objective-C

By Dave Mark, ©1997, All Rights Reserved. http://www.spiderworks.com

Well, it finally happened. Apple made their OS decision, catching many of us by surprise. Personally, I am very excited by Apple's move. As was clear from the energy at Macworld Expo, things are finally moving. Apple has made a bold move. Now we have to retool and rethink our programming strategies.

As Apple made clear, the System 7.5 version of the Mac Toolbox still has some significant legs and will likely be part of our lives for some time to come. As I write this, the announced release schedule for Rhapsody (code name for the new OS) does not show a significant beta in our hands until January of next year. Nothing to complain about there. Of course, it will take time for Apple to marry their technology to that of NeXT and we all want this job done right.

My point is that there are some important decisions we all have to make, but the current schedule gives us the luxury of continuing down the current path (System 7.5 apps) without penalty, while giving us the time to plan for the new order.

What About Be?

Before we move on to the main focus of this column, I'd like to take a second to talk about the apparent loser in the OS wars: Be, Inc. You might think that because Be was not able to work out a deal with Apple, they have become damaged goods. Not so! As anyone who attended the first ever Be developer's conference will tell you, the BeOS is cool, the commitment from developers is there, and there's an excitement in the air, a feeling of being in on the ground floor of something big.

Bottom line, we now have two technological evolutions to follow. Things are about to get very interesting.

Java, C, C++, and Pascal vs. Objective-C

There are a number of questions raised by Apple's acquisition of NeXT. (See this month's Factory Floor interview with Avie Tevanian, Apple's new OS boss.) Among them, in what programming language will Rhapsody development be done? Is Objective-C the new sheriff in town? Will we be able to continue our C/C++ and Pascal efforts? And what about Java?

As we go to press, these issues are still not finalized. The story so far seems to be "all of the above." Objective-C is the language for NEXTSTEP, and should provide the most intimate access to Rhapsody. So far, it looks like C, C++, Pascal, etc. will all be supported, though in a slightly more distant relationship. Objective-C and Java support dynamic binding. C and Pascal support static binding, and C++ supports late binding.

In a nutshell, binding connects a called function to the function caller. Static binding means that the function being called is determined as the program is compiled. Though you can use function pointers to delay binding decisions in C, typically your binding decisions are made when you compile.

Dynamic binding is the opposite of static binding. The binding decision is delayed until runtime. This allows you to add components to your program while it is still running. If the runtime environment is designed to support this (and Rhapsody should be), it opens up a lot of interesting possibilities.

The C++ language supports a limited version of dynamic binding called late binding. In C++, a function call must type-match exactly the called function (called static typing) or else type-match exactly an inherited function. Though C++ virtual functions allow you to delay the binding until runtime, the type constraints still apply. Late binding is still restricted. Dynamic binding is unconstrained.

Java uses the same binding mechanism as Objective-C. Java offers the advantage of being a cross-platform solution, as well as tightly integrated with the Internet. It seems likely that Java will continue to grow and is likely to play a large role in Rhapsody.

What does all this mean for you? If you've been following this column over the past few months, you've already gotten a handle on Java. Over the next few months, we'll dig into Objective-C, starting with a review of some object programming terminology and a first look at the language syntax.

Finally, you can call the NeXT order desk at 800-TRY-NEXT (800-879-6398) to order books, manuals and software directly from NeXT, including "OpenStep Object-Oriented Programming and the Objective-C Language", "Enterprise Objects Framework Developer's Guide (for EOF 2.0)", "Working with Interface Builder (for Enterprise Objects Framework)", and "Discovering OPENSTEP: A Developer Tutorial (for Windows NT)."

Some Object Programming Terminology

Before we move on to the basics of Objective-C syntax, let's review a bit of object programming terminology, just to make sure we are all on the same page. We've already talked about dynamic, static, and late binding. Here are a few more.

Instances, methods, and instance variables. Just as in C++, an Objective-C class definition is a template for the creation of individual objects, also known as instances. The functions within a class (member functions) are known as methods, and the variables (data members) are known as instance variables.

Messages

In C++, an object's member function gets called. In Objective-C, a message is sent to an instance, known as the receiver. At runtime, the appropriate receiver method capable of handling the message is determined and the method is called.

Interface, implementation, and encapsulation

The interface to a class is the set of external methods defined for that class. The implementation is the internal workings of the class. The idea here is to keep the inner workings hidden from the user of a class, forcing them to access an instance via its interface. This mechanism is known as encapsulation. In Objective-C, all instance variables are encapsulated and access to them is limited to methods defined for the class.

Inheritance

Inheritance in Objective-C works pretty much as it does in C++. The parent class is known as a superclass and derived classes are known as subclasses.

A First Look at the Objective-C Language

Objective-C starts off with all the standard syntax of C. Objective-C source code files use the extension ".m", while header files stick with the extension ".h".

Objective-C features a generic object pointer type called id.

id myObject;

An id is designed as a generic pointer to an object's instance variables. The previous line of code didn't actually allocate an object. It created a pointer which will eventually be used to allocate the object. nil is defined as an id with a value of 0.

By using a generic object pointer type, Objective-C delays the type binding decisions until run time. This is a good thing, but it also puts a bit of extra overhead on the run-time system. Basically, in the NeXT world, all objects are derived from the root class Object. Object features an isa variable which is inherited by all Object subclasses (which should be all classes in your program). The isa instance variable specifies the class to which the object belongs.

Earlier, we talked about the separation of interface and implementation. In Objective-C, you declare the classes interface like this

 MySuperClass
{
 instance variable declarations
}
method declarations

Objective-C supports the standard C compiler directives that start with "#". In addition, Objective-C adds Objective-C specific compiler directives which start with "@". As you might expect, class names start with an upper case letter and variable names with a lower case letter. By convention, all identifiers are named using intercaps, yielding names like myVariable and MyClass.

Instance variable declarations are done just as they are in C and C++, though the type "id" is used pretty frequently in Objective-C and, obviously, is not built in to C or C++.

Method declarations are pretty funky. Here's a sample:

- (int)getX:(int)x andY:(int)y;

The leading minus sign marks this function as an instance method. A leading plus sign ("+") marks the method as a class method. (A class method is sort of like a static method in C++. We'll talk about class objects and class methods in a future column.)

The return type is specified in parentheses, just as if it were a typecast. If you leave off the return type, it defaults to the type id (just as a C function defaults to int if you leave off the return type). Note that a function that is not a method still defaults to a return type of int.

The name of the method specified above is getX:andY: and includes the colons in the name. Weird, eh? The idea is to have each chunk of the method end with a colon and correspond to a parameter. In this case, there are two parameters, x and y. The type of each parameter is also specified by a typecasting-like mechanism. Both x and y are ints.

Here's another example:

- getObj1:object1 andObj2:object2;

Note that this time all the type information was left out of the declaration. The return type and type of both arguments are the same, the default type "id".

Here's a sample class interface:

#import "Object.h"

 Object
{
 idmyVar;
}
- init;
- getLastObject:lastObject;

This interface declares a class named MyClass derived from the class Object. MyClass features a single variable, an id named myVar, and two methods, one named init and one named getLastObject, both of which return an id.

Note that the interface, which lives in a ".h" file, starts off with a #import compiler directive. #import replaces the #ifdef business you use in C++ to make sure you don't include an include file twice. Use #import to include any header files you need to include. Alternatively, you can just declare the classes you reference using the @class directive.


This directive tells the compiler that Object is a class. That's it. This delays any type analysis until run-time and can solve some knotty cross-dependancy problems where classes refer to each other. Bottom line, use the @class directive if you can get away with it, otherwise #import the classes' header file.

The implementation of a class looks like this:

 MySuperClass
{
 instance variable declarations
}
method definitions

Gee, doesn't this look familiar? Yup, the implementation looks almost identical to the interface. The differences? The implementation lives in a ".m" file instead of in a ".h" file and the method definitions replace the method declarations in the interface. Also, you are required to #import your classes' interface file in the implementation file. One nice benefit of this last fact is that you can leave the superclass and the instance variable declarations out of the implementation.

Here's another look:

#import "MyClass.h"

Till Next Month...

Hopefully, you've got a feel for the basic structure of an Objective-C program. Next month, we'll talk about message receivers and message syntax, and present our first Objective-C program. To get a head start, check out the Objective-C specification on the NeXT web site. (See the URL earlier in the column.) You can buy the NEXTSTEP environment running under NeXT, WinNT, and on top of Mach. Also, you might want to check out CodeBuilder from Tenon InterSystems. CodeBuilder runs on a Mac and comes with (among a LOT of other stuff) an Objective-C compiler. You might also want to check out Apple's web site to find out the current release schedule for Rhapsody tool betas and the Metrowerks web site to find the status of their Rhapsody tools.

 

Community Search:
MacTech Search:

Software Updates via MacUpdate

Latest Forum Discussions

See All

Pack a magnifying glass and practice you...
Somehow it has already been a year since Torchlight: Infinite launched, and XD Games is celebrating by blending in what sounds like a truly fantastic new update. Fans of Cthulhu rejoice, as Whispering Mist brings some horror elements, and tests... | Read more »
Summon your guild and prepare for war in...
Netmarble is making some pretty big moves with their latest update for Seven Knights Idle Adventure, with a bunch of interesting additions. Two new heroes enter the battle, there are events and bosses abound, and perhaps most interesting, a huge... | Read more »
Make the passage of time your plaything...
While some of us are still waiting for a chance to get our hands on Ash Prime - yes, don’t remind me I could currently buy him this month I’m barely hanging on - Digital Extremes has announced its next anticipated Prime Form for Warframe. Starting... | Read more »
If you can find it and fit through the d...
The holy trinity of amazing company names have come together, to release their equally amazing and adorable mobile game, Hamster Inn. Published by HyperBeard Games, and co-developed by Mum Not Proud and Little Sasquatch Studios, it's time to... | Read more »
Amikin Survival opens for pre-orders on...
Join me on the wonderful trip down the inspiration rabbit hole; much as Palworld seemingly “borrowed” many aspects from the hit Pokemon franchise, it is time for the heavily armed animal survival to also spawn some illegitimate children as Helio... | Read more »
PUBG Mobile teams up with global phenome...
Since launching in 2019, SpyxFamily has exploded to damn near catastrophic popularity, so it was only a matter of time before a mobile game snapped up a collaboration. Enter PUBG Mobile. Until May 12th, players will be able to collect a host of... | Read more »
Embark into the frozen tundra of certain...
Chucklefish, developers of hit action-adventure sandbox game Starbound and owner of one of the cutest logos in gaming, has released their roguelike deck-builder Wildfrost. Created alongside developers Gaziter and Deadpan Games, Wildfrost will... | Read more »
MoreFun Studios has announced Season 4,...
Tension has escalated in the ever-volatile world of Arena Breakout, as your old pal Randall Fisher and bosses Fred and Perrero continue to lob insults and explosives at each other, bringing us to a new phase of warfare. Season 4, Into The Fog of... | Read more »
Top Mobile Game Discounts
Every day, we pick out a curated list of the best mobile discounts on the App Store and post them here. This list won't be comprehensive, but it every game on it is recommended. Feel free to check out the coverage we did on them in the links below... | Read more »
Marvel Future Fight celebrates nine year...
Announced alongside an advertising image I can only assume was aimed squarely at myself with the prominent Deadpool and Odin featured on it, Netmarble has revealed their celebrations for the 9th anniversary of Marvel Future Fight. The Countdown... | Read more »

Price Scanner via MacPrices.net

Every model of Apple’s 13-inch M3 MacBook Air...
Best Buy has Apple 13″ MacBook Airs with M3 CPUs in stock and on sale today for $100 off MSRP. Prices start at $999. Their prices are the lowest currently available for new 13″ M3 MacBook Airs among... Read more
Sunday Sale: Apple iPad Magic Keyboards for 1...
Walmart has Apple Magic Keyboards for 12.9″ iPad Pros, in Black, on sale for $150 off MSRP on their online store. Sale price for online orders only, in-store price may vary. Order online and choose... Read more
Apple Watch Ultra 2 now available at Apple fo...
Apple has, for the first time, begun offering Certified Refurbished Apple Watch Ultra 2 models in their online store for $679, or $120 off MSRP. Each Watch includes Apple’s standard one-year warranty... Read more
AT&T has the iPhone 14 on sale for only $...
AT&T has the 128GB Apple iPhone 14 available for only $5.99 per month for new and existing customers when you activate unlimited service and use AT&T’s 36 month installment plan. The fine... Read more
Amazon is offering a $100 discount on every M...
Amazon is offering a $100 instant discount on each configuration of Apple’s new 13″ M3 MacBook Air, in Midnight, this weekend. These are the lowest prices currently available for new 13″ M3 MacBook... Read more
You can save $300-$480 on a 14-inch M3 Pro/Ma...
Apple has 14″ M3 Pro and M3 Max MacBook Pros in stock today and available, Certified Refurbished, starting at $1699 and ranging up to $480 off MSRP. Each model features a new outer case, shipping is... Read more
24-inch M1 iMacs available at Apple starting...
Apple has clearance M1 iMacs available in their Certified Refurbished store starting at $1049 and ranging up to $300 off original MSRP. Each iMac is in like-new condition and comes with Apple’s... Read more
Walmart continues to offer $699 13-inch M1 Ma...
Walmart continues to offer new Apple 13″ M1 MacBook Airs (8GB RAM, 256GB SSD) online for $699, $300 off original MSRP, in Space Gray, Silver, and Gold colors. These are new MacBook for sale by... Read more
B&H has 13-inch M2 MacBook Airs with 16GB...
B&H Photo has 13″ MacBook Airs with M2 CPUs, 16GB of memory, and 256GB of storage in stock and on sale for $1099, $100 off Apple’s MSRP for this configuration. Free 1-2 day delivery is available... Read more
14-inch M3 MacBook Pro with 16GB of RAM avail...
Apple has the 14″ M3 MacBook Pro with 16GB of RAM and 1TB of storage, Certified Refurbished, available for $300 off MSRP. Each MacBook Pro features a new outer case, shipping is free, and an Apple 1-... Read more

Jobs Board

*Apple* Systems Administrator - JAMF - Activ...
…**Public Trust/Other Required:** None **Job Family:** Systems Administration **Skills:** Apple Platforms,Computer Servers,Jamf Pro **Experience:** 3 + years of Read more
IT Systems Engineer ( *Apple* Platforms) - S...
IT Systems Engineer ( Apple Platforms) at SpaceX Hawthorne, CA SpaceX was founded under the belief that a future where humanity is out exploring the stars is Read more
Nurse Anesthetist - *Apple* Hill Surgery Ce...
Nurse Anesthetist - Apple Hill Surgery Center Location: WellSpan Medical Group, York, PA Schedule: Full Time Sign-On Bonus Eligible Remote/Hybrid Regular Apply Now Read more
Housekeeper, *Apple* Valley Village - Cassi...
Apple Valley Village Health Care Center, a senior care campus, is hiring a Part-Time Housekeeper to join our team! We will train you for this position! In this role, Read more
Sublease Associate Optometrist- *Apple* Val...
Sublease Associate Optometrist- Apple Valley, CA- Target Optical Date: Apr 20, 2024 Brand: Target Optical Location: Apple Valley, CA, US, 92307 **Requisition Read more
All contents are Copyright 1984-2011 by Xplain Corporation. All rights reserved. Theme designed by Icreon.