#iostips

What's the first thing that comes to mind when Constants is said to you? Immutable. Nothing can be changed. We usually assign constants to something that we do not alter at all. But I discover something pretty cool about Constants! Before this, I always thought once you assign anything to Constant, they are immutable. Check out the video, then the explanation below:

Lines 5 - 7

Basically just creating a constant variable called ironMan. It's just to show you that constants are immutable, as seen by the error given by Xcode.

Lines 11-25

This section shows about the class object Iron Man. It basically has a constant property called name of type String, and a variable occupation of optional String. As you can see, when we try to reassign ironMan2 constant name, it gave us an error. However, we can still alter the variable occupation optional string!

So, what's happening here? 

The constant iron3 (should have been iron man 3...sorry folks) is basically a pointer to that particular object, which you cannot alter. Nonetheless, you can still change the variable property of the constant object being pointed to.

Line 29-41

This section is to show Structs are completely immutable when declared as a constant. This can be seen at the error shown on line 41.

Why?

A couple of tutorials ago where iDrawCode covered the difference between Structs and Classes may help. The key is: When we assign the constant of the struct, we are copying the value. However, for classes, we are making reference to the class, which points to it in memory, and hence, allows us to make changes to the variables in the object.

Well, that's a quick one, but hopefully a useful one when you encounter Constants in the future. Hope you are enjoying my video formats too! =]