Dot notation with DllStruct fails if the variable is a constant

[genius257]

The code below illustrates the problem

#AutoIt3Wrapper_Run_Au3Check=N
Global Const $tStruct = DllStructCreate("BYTE a")

Works()
Fails()

Func Works($tStruct = $tStruct)
    $tStruct.a = 1
EndFunc

Func Fails()
    $tStruct.a = 1
EndFunc

Output

"D:\Desktop\tmp.au3" (12) : ==> Cannot assign values to constants.:
$tStruct.a = 1
^ ERROR

[Jos]

What exactly is the issue with getting a warning when trying to change a constant?

Jos

[genius257]

I'm not changing the constant, but a property of the constant.
If it should fail, so should DllStructSetData($tStruct, "a", 1)

[Jos]

The left $tStruct in Func Works() is a local declared variable for Func Works() and it act like doing it this way:

Global Const $tStruct = DllStructCreate("BYTE a")

Works()
Fails()

Func Works($x = $tStruct)
    $x.a = 1
EndFunc

Func Fails()
    $tStruct.a = 1
EndFunc

So $tStruct in Func Works() is not the Global declared one but a Local new variable.

Jos

[genius257]

I can't seem to find any details about how a constant in AutoIt is treated other than the value of a constant cannot be changed.

But currently AutoIt allows properties to be changed in constant variables if for instance it's a DllStruct and DllStructSetData is used. This is like ES6 when defining a const with a object value. Properties of the object can still be changed. The only thing that's immutable is the binding ​source.

If AutoIt is not supposed to act like my example with ES6, then AutoIt should not allow DllStructSetData to work with a constatnt variable as it's first parimeter.

If on the other hand the ES6 example is the case, then AutoIt should allow properties of const variables to be changed when using dot notation.

I hope I've made myself understandable and that you see the current way it works is a bug one way or the other?

[Melba23]

Dot notation for structs is an undocumented feature and so bug reports about the feature are not supported. Use DllStructSetData instead.

M23