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How to understand the syntax of message with multiple arguments in Objective C?

Answer 1

+3 A:

Trying for shortest answer:

Yes :)

Chris Kimpton 2010-08-16 08:44:29

OK then, I guess I can live with it.

aXqd 2010-08-16 09:38:42

Answer 2

+2 A:

I think that you are trying to understand objective-c associating it with OOP programming languages like Java or C++, which I don't recommend. With time passing you will understand and like the Objc approach, it took me 6 months to really enjoy it, and now I only enjoy ObjC development :p.
Anyway the ObjC man. says the following:

The method’s actual name (insertObject:atIndex:) is a concatenation of all of the signature keywords, including colon characters. The colon characters declare the presence of a parameter. If a method has no parameters, you omit the colon after the first (and only) signature keyword. In this example, the method takes two parameters.

Source: Methods and Messaging

Edit
The ObjC way of naming its methods, I like it better because I don't have to think about a method name, but about what messages ("represented by other objects") I want to send to object A so that I get what I want from it;

NSArray *list = [object_a fromCategory:@"Literature" authorsStartingWith:@"Em"];

or

NSArray *list2 = [object_a fromCategory:@"Literature" authorsStarginWith:@"EM" fromCentury:@"16"]

Try to use natural language and translate the message to object_a, something like: "Hey object a give me from category Literature all the authors stargin with "em" and which are from cetury 16" - This is the Message - you don't need a separate method Name - all together can be seen as a method name (as the man says).
Do you get now how elegant and Clear is ObjC way to do what you used to call "method overloading"?

Andrei T. Ursan 2010-08-16 08:44:59

ObjectiveC is nearer classic OOP (e.g Smalltalk) than most other languages

Mark 2010-08-16 08:53:46

Actually, Objective C is much closer to "classic" OOP than languages like C++ and Java. The method naming syntax is pretty much identical to Smalltalk's method naming syntax, and the programming model is truer to Smalltalk than C++ and Java.

JeremyP 2010-08-16 08:54:52

By classic oop I meant the Java and C++, because they are the industry standard, but I will edit my answer to be more clear.

Andrei T. Ursan 2010-08-16 08:57:03

There is no logical reason why I would say "Give me from category Literature the authors starting with 'Em'" rather than "Give me all the authors starting with 'Em' from the category Literature" — nor is there any reason I might name the the category and the first letters of the author's name, *or* the category and first letters of the authors name and the century, but would *never* name the category and the century *without* a prefix for the author's name. For a real-world example, I can never remember the argument order for NSWindow's designated initializer. There's nothing elegant about it.

Chuck 2010-08-16 09:10:11

Also, you seem to be comparing it to C++ and Java, but the example he gave is more like Python, which has proper keyword arguments. See here: http://docs.python.org/release/1.5.1p1/tut/keywordArgs.html — It really is syntactically and semantically superior IMO

Chuck 2010-08-16 09:16:29

[Order] is one thing. [Required and Optional] is another.

aXqd 2010-08-16 09:39:41

Answer 3

+3 A:

It's easier to implement because then selectors really are just the method's "name" as a string and the arguments can just be passed to the method in the order they were given. This allows Objective-C to be written easily as essentially a small preprocessor + set of runtime functions on top of C, which it originally was. To do it otherwise would be more complex.

It's also simpler because Objective-C's messaging syntax was derived from Smalltalk, which used the exact same way of doing selectors (though it was not a preprocessor to C), so this is zero change from the Smalltalk syntax.

You seem to be asking why Objective-C didn't take its design cues from languages that came into vogue many decades later. The answer would be: Because they weren't around yet. (I'm not sure if keyword arguments were common in Lisp by that time, but they weren't in most programming languages.)

Chuck 2010-08-16 09:01:47

yea, maybe you are right. iPhone is fashion, but Objective C is certainly not :P

aXqd 2010-08-16 09:27:22

hi, Chuck, I reconsidered the 1st paragraph of your comment. I don't see how hard it could be. After all, we have introduced a new syntax for message passing. I am not asking for the modern 'keyword argument' here. If we can not change the order, it's fine. All I want is just to give the 1st argument a separate name as what we can do to the 2nd, the 3rd...arguments.

aXqd 2010-08-16 11:28:27

You're not giving the arguments separate names. There's only one selector. By convention, the sections name the arguments that go after, but that connection is not inherent. I think you're really asking why we can't stick a space an an arbitrary position in the first logical section of the selector. That would actually be *inconsistent*. You can't stick a space in any other arbitrary position. You can only separate the selector at the colons, where arguments go. *Could* the language have been designed to include this inconsistency? Sure. But it wasn't, and it makes little difference.

Chuck 2010-08-16 11:39:54

Thanks, I finally got it. Yes, in the perspective of selector, adding a separate message name for it would actually be inconsistent. There's only one selector, hence we should regard both the message name and all the arguments as a whole to be the selector, e.g. [receiver] - [myRectangle], [selector] - [setOriginX:Y]. That make sense. :)

aXqd 2010-08-17 02:40:05

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How to understand the syntax of message with multiple arguments in Objective C?

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