How can AutoHotkey instance variables be used in WinTitle parameters? - autohotkey

Question

Let's say I have a function to get the window title of a process using its HWND id:
GetWindowTitle(hwnd) {
WinGetTitle, title, ahk_id %hwnd%
return title
}
So far, so good. It works like a charm. So, let's say I am trying to wrap some functionality within a class, in this fashion:
class RunningProcess {
hwnd := ""
windowTitle := ""
__New(hwnd) {
this.hwnd := hwnd
this.windowTitle := GetWindowTitle()
}
GetWindowTitle() {
WinGetTitle, title, ahk_id %this.hwnd%
return title
}
}
The aforementioned code fails to load with the following message:
The following variable name contains an illegal character: "this.hwnd".
I have tried several alternatives in order to use the instance variable hwnd as a WinTitle argument in WinGetTitle, to no avail. The only one that works for me involves using a local variable which grabs the contents of this.hwnd and then using the local variable as a WinTitle argument, like this:
GetWindowTitle() {
foo := this.hwnd
WinGetTitle, title, ahk_id %foo%
return title
}
However, this is less than ideal, as you might guess, at least in my opinion.
Is there a way to use this.hwnd as a WinTitle argument right off the bat?
Thanks!

Answer 1

I'd call it a classic case of having trouble with the legacy vs modern expression syntax.
Refreshing to see it this way though, usually people with the issue are writing 2007 level AHK, but nice to see you're writing modern AHK.
So anyway, forget about using %% to refer to variables. That's the legacy AHK way. In a modern expression statement you just type the name of the variable to refer to is, for example your assignments with the := operator are just fine that way, because it's using the modern expression syntax (= to assign would be the legacy way)
However, pretty much all commands, that haven't been replaced with more modern function, still use the legacy syntax on every parameter (unless otherwise specified in the documentation).
So, you're going to have to set the parameter to evaluate an expression, instead of expecting a legacy text parameter. To do that, you start off the parameter with a single % followed up with a space.
So your WinGetTitle command should look like this:
WinGetTitle, title, % "ahk_id " this.hwnd
Quotation marks around ahk_id , because that's how you specify a string in an expression, and then just type in the variable you want to concatenate to that string. The concatenation operator . could be used here like so % "ahk_id " . this.hwnd, but it's totally redundant and looks weird in my opinion as well.
Also, your call to the GetWindowTitle() function in the initializer __New is going to need a this. in front of it.
And initializing the instance variables to nothing is redundant as well. You can remove that if you want.
Finished product:
MyCoolObject := new RunningProcess(WinExist("A"))
MsgBox, % "The handle of currently active window is: " MyCoolObject.hwnd "`nAnd its title is: " MyCoolObject.windowTitle
class RunningProcess
{
__New(hwnd)
{
this.hwnd := hwnd
this.windowTitle := this.GetWindowTitle()
}
GetWindowTitle()
{
WinGetTitle, title, % "ahk_id " this.hwnd
return title
}
}
To learn more about legacy syntax vs expression syntax, see for example this page from the documentation:
https://www.autohotkey.com/docs/Language.htm