Computed properties

Getting Started
1

Hello,

I just discovered the existance of Computed Properties.
There are some interesting possibillities whith these properties.

Is there a reason why I should not use all my properties as computed properties.
Perhaps slowing down the program ?
Or are there other disadvantages ?

Regards
Etienne

2

That’s a lot of extra work for no gain if all you’re doing is storing and retrieving a value. While I haven’t tested, I’d expect it to be slower too, although I doubt you’d notice it unless your app’s speed is critical.

There is one exception. Xojo currently has no way to break if a property value changes but you can fake that by using a computed property and setting a breakpoint in its Set.

BTW, note that you don’t have to add code to a computed property’s Set and Get. Rather, by using only one, you can create a read-only or write-only property.

3

You do have to have a “GET”, but not a “SET”
Computed properties cannot have parameters (ie. Arrays etc)
for those you would use Overloaded Functions

But for the most part you would use these

  • where you wanted a READ ONLY varaible (
  • A variable that would be allowed to be SET only under certain circumstances, or to provide an EVENT when changed
4

You can set just the Set, Dave, you don’t have to have a Get. Try it.

5

And this is one of the problems with working in multiple disciplines at the same time :slight_smile:

SWIFT is what doesn’t allow SET only “Variable with a setter must also have a getter”

6

This is indeed a very nice way to look for property changes.

Question : I changed a property to a computed property → Ok
But how can I return this property to normal again ?

I think these are good suggestions when using Computed Properties.

Thanks for all the replys

Regards
Etienne

7

You can’t revert a computed property directly. Delete it and add back a regular property with the same name or, if there is a shadow property, rename that and set its scope.