This is one of the first questions when starting to learn Scala. There seems to be two types of variables. Why? The reason is actually quite brilliant and even though I have worked in a dozen of other languages I have not seen it before. The reason is the we as programmers often make constant variables. This is in itself a contradiction so in Scala they are simply called Values, or Val so once it is set it cannot be changed:
Here you can see I define a value to be speed of light. This is something I probably will not change in the duration of my program so I will make it a val. If I try to change it the compiler will complain.
If this was a regular variable I would be allowed to change the value and perhaps mess up an important calculation:
Maybe I meant speed of flight (shrug). Anyway now it is all f’ed up.
Other languages have the same idea but I cannot remember seeing it as clearly separated as in Scala.
We usually say the var is mutable and val is immutable but I prefer variable and value or constant. Why put a bow on it?