AKMA’s Random Thoughts

I did the same thing with a similar headline in the LA Times!

Margaret, great minds think alike!

Actually, I like Margaret's version better.

When Batman went home at the end of a night spent fighting crime, he put on a suit and tie and became Bruce Wayne. When Clark Kent saw a news story getting too hot, a phone booth hid his change into Superman. When you're programming, all the variables you juggle around are doing similar tricks as they present one face to you and a totally different one to the machine.

We can see an example of this in our code we've written so far. In each function's block, we declare variables that hold our data. When each function ends, the variables within are disposed of, and the space they were using is given back to the computer to use. The variables live in the blocks of conditionals and loops we write, but they don't cascade into functions we call, because those aren't sub-blocks, but different sections of code entirely. Every variable we've written has a well-defined lifetime of one function.

For this program, it was a bit of overkill. It's a lot of overkill, actually. There's usually no need to store integers in the Heap, unless you're making a whole lot of them. But even in this simpler form, it gives us a little bit more flexibility than we had before, in that we can create and destroy variables as we need, without having to worry about the Stack. It also demonstrates a new variable type, the pointer, which you will use extensively throughout your programming. And it is a pattern that is ubiquitous in Cocoa, so it is a pattern you will need to understand, even though Cocoa makes it much more transparent than it is here.

Inside each stack frame is a slew of useful information. It tells the computer what code is currently executing, where to go next, where to go in the case a return statement is found, and a whole lot of other things that are incredible useful to the computer, but not very useful to you most of the time. One of the things that is useful to you is the part of the frame that keeps track of all the variables you're using. So the first place for a variable to live is on the Stack. This is a very nice place to live, in that all the creation and destruction of space is handled for you as Stack Frames are created and destroyed. You seldom have to worry about making space for the variables on the stack. The only problem is that the variables here only live as long as the stack frame does, which is to say the length of the function those variables are declared in. This is often a fine situation, but when you need to store information for longer than a single function, you are instantly out of luck.

When Batman went home at the end of a night spent fighting crime, he put on a suit and tie and became Bruce Wayne. When Clark Kent saw a news story getting too hot, a phone booth hid his change into Superman. When you're programming, all the variables you juggle around are doing similar tricks as they present one face to you and a totally different one to the machine.

The rest of our conversion follows a similar vein. Instead of going through line by line, let's just compare end results: when the transition is complete, the code that used to read: