Re: Garbage collection - was Beginner with Cocoa

FROM : Erik Buck
DATE : Mon Mar 24 17:12:36 2008

> In Ruby GC just works dandy without thought. Why is it so different in
> Cocoa Obj2.0?
> What kinda of real headaches will I have jumping into osx programing
> compared to ruby ?


The short answer is that Ruby is a nifty high level scripting language 
that insulates the programmer thoroughly from pointers and memory 
management.  In contrast, C is a low level "systems" programming 
language that relies on pointers.  Many things you might want to 
program require the low level capabilities of C.  For example, I bet 
the Ruby garbage collector is written in C.  Operating systems, device 
drivers, high performance graphics, etc. all use close to the hardware 
features provided by C but absent from Java, Ruby, Python, C#, etc.

Objective-C is a combination of the original object oriented language, 
Smalltalk, and C.  The Smalltalk heritage is what makes Objective-C/
Cocoa programming so powerful and flexible.  The C heritage is what 
makes Objective-C/Cocoa so versatile and able to seamlessly integrate 
with the billions of lines of C code in the world.

With C comes pointers.  With the availability of arbitrary pointers 
and pointer arithmetic, it is basically impossible to provide 
ubiquitous automatic garbage collection.  Therefore, Objective-C will 
always be saddled with edge cases where garbage collection will be 
messy or at least not automatic.  Furthermore, there are lots of 
applications in which Objective-C can be used but automatic garbage 
collection can not.  For example, memory and resources that are not 
allocated from the heap, such as shared memory, VRAM, distributed 
objects, etc. can not be automatically collected.

Ruby solves the "what to do with uncollectible resources" problem by 
just not letting you access them.  You won't see a high performance 3D 
game engine written in Ruby any time soon!  You will see Ruby 
libraries built to use a 3D engine written in C or Objective-C.