objective-c. How to work with immutable Dictionary and return a copy? - objective-c

Question

I'm new in objective-c
The idea is that I'm passing a Dictionary to a method that return an altered Dictionary back.
I have a human "breath" method that expects as argument "air" Dictionary and returns another "air" dictionary.
test
-(void)testBreathIsConsumingTheRightAmountOfOxygen {
NSDictionary *oldAir = [[Environment alloc] init].air;
NSDictionary *newAir = [self.hummy breath:oldAir];
XCTAssertEqual([[newAir valueForKey:#"O2"] intValue], 995);
}
-(void)testBreathIsProducingTheRightAmountOfDioxide {
NSDictionary *oldAir = [[Environment alloc] init].air;
NSDictionary *newAir = [self.hummy breath:oldAir];
XCTAssertEqual([[newAir valueForKey:#"CO2"] intValue], 5);
}
code (my pour solution, I don't like it)
- (NSDictionary *) breath: (NSDictionary *) air {
int breathingStep = 5;
int oxygenOut = [[air valueForKey:#"O2"] intValue] - breathingStep;
int dyoxideOut = [[air valueForKey:#"CO2"] intValue] + breathingStep;
NSMutableDictionary *newAir = [NSMutableDictionary dictionaryWithDictionary:air];
[newAir setValue:[NSNumber numberWithInt:oxygenOut] forKey:#"O2"];
[newAir setValue:[NSNumber numberWithInt:dyoxideOut] forKey:#"CO2"];
return [NSDictionary dictionaryWithDictionary: newAir];
}
The *air Dictionary looks like this
[NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithInt:1000], #"O2", [NSNumber numberWithInt:0], #"CO2", nil ]

Answer 1

As a side note you should really be using the modern Objective-C syntax when dealing with NSDictionary and NSNumber.
I think you're looking for the mutableCopy method which returns a mutable version of the current dictionary.
- (NSDictionary *)breath:(NSDictionary *)air {
int breathingStep = 5;
NSMutableDictionary *newAir = [air mutableCopy];
newAir[#"O2"] = #([air[#"O2"] intValue] - breathingStep);
newAir[#"CO2"] = #([air[#"CO2"] intValue] + breathingStep);
return [NSDictionary dictionaryWithDictionary:newAir];
}
To make this better the keys (O2 and CO2) should be constant, for example:
NSString *const kBreathO2Key = #"O2";
NSString *const kBreathCO2Key = #"CO2";
Usage would be:
newAir[kBreathO2Key] = #([air[kBreathO2Key] intValue] - breathingStep);
To make this even better again it may be more appropriate to create a class to hold these values rather than a dictionary. Then you wouldn't need to convert between NSNumber and int.
#interface ASAir : NSObject
#property (nonatomic, assign) NSInteger O2;
#property (nonatomic, assign) NSInteger CO2;
#end
#implementation
#end
Then the breath: method could be improved as follows:
- (ASAir *)breath:(ASAir *)air {
int breathingStep = 5;
ASAir *newAir = [[ASAir alloc] init];
newAir.O2 = air.O2 - breathingStep;
newAir.CO2 = air.CO2 + breathingStep;
return newAir;
}