Why should I use asserts?

Question

I never got the idea of asserts -- why should you ever use them?

I mean, let\'s say I were a formula driver and all the asserts were things like security belt, helm

Answer 1

In Code complete is a section that says something like. Every time you write an if without any else you are maybe missing something.

It is like this code

int i = 1
i = i++ 

The common programmer will never think about what happens if i is negative in later code. There is the slightly chance of your code producing an overflow and languages like java will jump from max int to min int and you get a very big negative number. This are all the cases you normally say. Uh this will never ever happen. But what is your program doing if it happens? So if you know that there is something that you think will never happen test for it or against it and put an assert false in the else clause that will never happen instead of don't program the else statement. In this way your program should crash completely in the moment you aren't sure any more what it is doing. In production code there should be something different from rather crashing something like informing the user, the maintainer and then exiting.

Another use of assertions is contract driven design. You specify an contract with your interface and depending on your place in the program you assert your input but much more importing you are asserting your output two.

I agree with you that disabled assertions in production code make assertions rather useless. And the default assertions off in case of the java vm is a hazard in my opinion.