about "setTo" and "over"

[zhangfeng]

Hello.

I'm reading the second edition of "Programming in Objective-C 2.0". The following code in "Synthesized Accessor Methods" of Chapter 7 confused me.

Code: (Objective-C)

@interface Fraction : NSObject
{
int numerator;
int denominator;
}

@property int numerator, denominator;

-(void) print;
-(void) setTo: (int) n over: (int) d;
-(double) convertToNum;
@end

I have 2 questions:

1, What's the meaning of setTo and over? I deleted "-(void) setTo: (int) n over : (int) d", and the program works well.

2, If there are more than 2 instance variables, how do we rewrite this sentence?

Thanks!

[skochan]

You'll recall that setTo:Over: was a method we developed that allowed you to set a fraction's numerator and denominator in a single method call.   There is no way to synthesize a method for more than one property (that is, a method that takes multiple arguments).

Cheers,

Steve Kochan

[zhangfeng]

You'll recall that setTo:Over: was a method we developed that allowed you to set a fraction's numerator and denominator in a single method call.   There is no way to synthesize a method for more than one property (that is, a method that takes multiple arguments).

Cheers,

Steve Kochan

Thanks for your answer.

If I don't want to set a fraction's numerator and denominator in a single method call, can  setTo: over: be deleted from the program like this?

Fraction.h

Code: (Objective-C)

#import <Foundation/Foundation.h>


@interface Fraction : NSObject {
	int numerator;
	int denominator;
}

@property int numerator, denominator;

-(void) print;
//-(void) setTo: (int) n over: (int) d;
-(double) convertToNum;
@end

Fraction.m

Code: (Objective-C)

#import "Fraction.h"

@implementation Fraction

@synthesize numerator, denominator;

-(void) print
{
	NSLog(@"%i/%i", numerator, denominator);
}

-(double) convertToNum
{
	if (denominator != 0) 
		return (double) numerator / denominator;
	else 
		return 1.0;
}
@end

FractionTest.m

Code: (Objective-C)

#import "Fraction.h"

int main (int argc, const char * argv[]) {
    NSAutoreleasePool * pool = [[NSAutoreleasePool alloc] init];
	
    Fraction *myFraction = [[Fraction alloc] init];
	
	//set fraction to 1/3
	[myFraction setNumerator: 1];
	[myFraction setDenominator: 3];
	
	//display the fraction
	NSLog(@"The value of myFraction is:");
	[myFraction print];
	[myFraction release];
	
    [pool drain];
    return 0;
}

And sorry for my bad English. I can't understand "There is no way to synthesize a method for more than one property (that is, a method that takes multiple arguments).". In this example, we can set 2 instance variables using 1 method. Why we can't synthesize a method for more than property?