Question

In Objective-C 2.0, is it possible to make a method where the argument is optional? That is, you can have a method call like this:

[aFraction print]; 

as well as this:

[aFraction print: someParameter]; 

in the same program.

Apple’s Objective-C 2.0 Programming Language guide contrasts Obj-C with Python and seems to say this is not allowed. I’m still learning and I want to be sure. If it is possible, then what is the syntax, because my second code example does not work.

Update: OK, I just made two methods, both named ‘print’.

header

-(void) print; -(void) print: (BOOL) someSetting;  

implementation

-(void) print {     [self print:0]; }  -(void) print: (BOOL) someSetting {     BOOL sv;     sv = someSetting;      if ( sv ) {         NSLog(@'cool stuff turned on');     }     else {         NSLog(@'cool stuff turned off');     } } 

the relevant program lines

    ...     printParamFlag = TRUE;  // no parameter     [aCodeHolder print];  // single parameter     [aCodeHolder print:printParamFlag];     ... 

I can’t believe that worked. Is there any reason I shouldn’t do this?

Answer 1

You can declare multiple methods:

- (void)print; - (void)printWithParameter:(id)parameter; - (void)printWithParameter:(id)parameter andColor:(NSColor *)color; 

In the implementation you can do this:

- (void)print {     [self printWithParameter:nil]; }  - (void)printWithParameter:(id)parameter {     [self printWithParameter:nil andColor:[NSColor blackColor]]; } 

Edit:

Please do not use print and print: at the same time. First of all, it doesn’t indicate what the parameter is and secondly no one (ab)uses Objective-C this way. Most frameworks have very clear method names, this is one thing that makes Objective-C so pain-free to program with. A normal developer doesn’t expect this kind of methods.

There are better names, for example:

- (void)printUsingBold:(BOOL)bold; - (void)printHavingAllThatCoolStuffTurnedOn:(BOOL)coolStuff;