Question

Hopefully this will not come across as a silly or pedantic question, but I’m curious.

Occasionally I’ll be in a situation where an existing object’s properties may need to be updated with new variables, and I’ll do it like this (in no particular language):

public void Update(date, somevar){
 if(date > this.Date){
  this.Var = somevar;
 }
}

The idea being that if the date passed to the function is more recent than the date in the current object, the variable is updated. Think of it as like a basic way of caching something.

Now, the interesting part is that I know somevar will never be “old” when compared to this.Var, but it may be the same. So as far as I can see, checking the date is pointless, and therefore a pointless operation for the program to perform.

So what this is really about is whether it’s better – in whatever way – to perform a write to this.Var every time Update is called, or getting this.Date, comparing it, then possibly performing the write. And just to throw in something interesting here, what if Update were to be called multiple times?

If the example I’ve given makes no sense or has holes in it, I apologise; I can’t think of another way of giving an example, but hopefully you can see the point I’m trying to make here.

Answer 1

Unless for some reason assignment is an expensive operation (e.g. it always triggers a database write), this isn’t going to make your programme faster.

The point of putting checks in your setters is usually to enforce data integrity, i.e. to preserve programme invariants, and thus the correctness of your other code, which is rather more important.