NSArray multiply each argument

Question

Is the there a way to multiply each NSNumber contained in the array by 10? Here is what I have so far:

NSMutableArray *vertex = [NSMutableArray arrayWithCapacity:3];

[vertex addObject:[NSNumber numberWithFloat:1.0]]; 
[vertex addObject:[NSNumber numberWithFloat:2.0]];
[vertex addObject:[NSNumber numberWithFloat:3.0]];

[vertex makeObjectsPerformSelector:@selector(doSomethingToObject:)];

I am not sure what selector to use to do this, please help!

Answer 1

Not easily, no. You would have to loop through the entire thing and replace all those instances of NSNumber with new instances of NSNumber (NSNumber itself is immutable). So, for example:

for( int i = 0; i < [vertex count]; i++ )
  [vertex replaceObjectAtIndex:i withObject:[NSNumber numberWithFloat:[[vertex objectAtIndex:i] floatValue] * 10.0f]];

Obviously this is rather hard to read. You are probably better off just using a regular, primitive array of floats if you are going to be manipulating them often (e.g., applying transformations to them).

Answer 2

Short answer - no.

NSNumber of merely a container for a primitive value. It does not do any mathematical work. The makeObjectsPerformSelector method can be used to tell each object in the array to do something. But the class of each of those objects has to have the method the selector is for. NSNumber also does not provide any method for changing the stored value. So even if you added a category to NSNumber to do the math, you would still have to replace the old value in the array with the newly computed one.

I think a better solution would be to add a category method to NSMutableArray to do the work. It would look through the contents, calculate each new value and then replace each array member with the new one.