`count` seems to be used very consistently for collections of undefined types in Cocoa. See `NSArray`, `NSSet`, `NSMapTable`, etc.

The `numberOf<whatever>` pattern seems prevalent when the container is specific for objects of a contained type: `numberOfRows`, `numberOfItems`, `numberOfLines`, `numberOfPages`, `numberOfGlyphs`, `numberOfPlans`, `numberOfTouches`, `numberOfSections`, `numberOfButtons`, `numberOfColumns`, etc. (the list actually goes on and on)

So in short I thought about it and this seemed more idiomatic.