Article:		The Objective-C Language
Subject:		Question
Date:		2001-05-08 12:38:40
From:		uwiz
I have a question concerning the following syntax: - (void)setXLocation:(double)x yLocation:(double)y I don't understand the yLocation:(double)y part. Isn't yLocation an instance variable in the given example? Why is an instance variable listed in a method declaration? thanks

Showing messages 1 through 7 of 7.

• Question
  2001-05-08 15:20:23  Michael Beam | [View]
  
  
  P.S. In the method under scrutiny here, the name of the method without the arguments is:
  
  setXLocation:yLocation:
  
  So you see yLocation here isn't refering to the instance variable, but is just part of the name. Also, the reason we have uppercase "X" and lowercase "y" is purely a matter of aesthetics. If the arguments were reversed then I would have written an uppercase "Y" and lowercase "x":
  
  setYLocation:xLocation
  
  I just like having new words or standalong letters in variable and method names start with an uppercase letter. Purely a matter or preference.
  
  
  
  Sorry if this was redundant with my last message, i'm just trying to attack it from all angles.

• Question
  2001-05-08 15:12:51  Michael Beam | [View]
  
  
  Yes, yLocation is an instance variable for the class. "yLocation" the text is also part of the method name described. The reason i choose this name is to provide information about what the argument following the colon sets. you could have replaced "yLocation:(double)y" in the method declaration with "locationOfYCoordinate:(double)y" if you wanted. I just choose "yLocation" because ultimately that is the instance variable being set to the value of the second argument in this method.
  
  hope that helps clear things up!
  
  Mike
  
• Question
  2001-05-10 14:41:38  kcrawford [View]
  
  
  I'm still confused. You put the arguments inside the name of the method?
  
  Please show the same method written in Java so I can translate.
  
  Would it be:
  
  public void setXLocationyLocation(double x, double y){}
• Question
  2001-05-11 06:13:54  Michael Beam | [View]
  
  
  that's right, you put arguments in the name of the method. Think of it as each argument having a label that is part of the method name. Your java line was correct, although i think you meant to put in a Y before the second location
  
  public void setXLocationYLocation(double x, double y) {}
  
  
• Question
  2001-05-11 09:19:15  kcrawford [View]
  
  
  Thanks, that clears things up a bit.
  
  Would you call the method with multiple arguments the same way--with the arguments inside the method name?
  
  For example, would you call the method
  
  - (void)setXLocation:(double)x yLocation:(double)y
  
  like this
  
  [setXLocation:10 yLocation:20];
• Question
  2001-05-11 12:00:20  Michael Beam | [View]
  
  
  Yeah, that's right, except your method call has no receiver, and it should. So it would have to be
  
  [anObject setXLocation:10 yLocation:20];
  
  when you want to invoke it.
• Question
  2001-05-15 10:06:53  TheBum [View]
  
  
  Allow me to step in here with a related question if I may. Are the tags in the argument list of the declaration, e.g. yLocation, just for readability or do they provide a way of specifying arguments in any order?