How the ByRef acts in this scenario?

[czardas]

Null is not a variable, so your example has only a vague association with my comment which you quoted above. You are doing something which has not been documented, and the behaviour you are seeing is perhaps the result of some internal code which has somehow avoided the radar of detection. There's something going on and we don't know what it is.

[Guest]

I think I get it -

If I pass non-variable then it allocate new memory.  otherwise it will reference to the source variable.
correct?

Which seemed odd to me is why it accepted non-variable at the first place.. so jchd said that it was a " a feature request already made".. I don't know what is the point of this feature..

Now I understand correctly the story?

Edited April 18, 2017 by Guest

[jchd]

No, I referred to a recent post about optional ByRef args, see this ticket https://www.autoitscript.com/trac/autoit/ticket/3540

 

[TheDcoder]

Rings some bells

 

[Guest]

5 hours ago, jchd said:

No, I referred to a recent post about optional ByRef args, see this ticket https://www.autoitscript.com/trac/autoit/ticket/3540

 

What about this:

Quote

If I pass non-variable then it allocate new memory.  otherwise it will reference to the source variable.
correct?

 

[jchd]

Of course that's correct. Else how do you think you could "pass something" without allocating memory? C and friends use the program stack, AutoIt allocates a hidden variable (variant) for storing the "non-variable" (here I interpret that term as "a literal"). In all cases you have to store a value in a chunk of memory to pass it away.

Few programming languages rely entirely on white magic.

[Guest]

Yes, I know it must be true .. I just asked anyway in case there is a magical surprise

[trancexx]

The interpreter works like this (line by line):

; I am the interpreter!

SomeFunc(Null)  ; I need to call SomeFunc. First let me check that the function exist. Oh great, it does, found it in list of all functions that I created at the beginning!
                ; Ok I need to create the list of arguments for this call, the user is passing one parameter.
                ; The list of arguments will therefore have one member.
                ; Let me first create unnamed variable (because user passes literal) with value of Null. Done!
                ; Time for the list of arguments...
                ; Hm, I see that inside definition of SomeFunc the first argument is ByRef, so I'll add reference to the unnamed variable I created moment ago to the list. Dang bang... done!
                ; Calling the function now.

Func SomeFunc(ByRef $Output)
    ; I'm inside a function and I have one local variable named $Output to work with plus no global variables. This $Output is ByRef, so
    ; I won't be allocating anything.
    $Output = 1 ; The user is changing the value of $Output variable. I see that $Output is reference. Accessing the original variable... changing... Done!
    ;...
    ConsoleWrite($Output & ' (L: ' & @ScriptLineNumber & ')' & @CRLF) ; This will print 1
EndFunc

More clear?

[czardas]

So to get an optional ByRef parameter, all you have to do is alter this part.

; Let me first create unnamed variable (because user passes literal) with value of Null. Done!
; Let me first create unnamed variable (because user passes nothing) with value of nothing. Done!

; Edit - I forgot to include the next line.
; Assign default value to unnamed variable. Done!

Is that right?

Edited April 20, 2017 by czardas

[jchd]

@trancexx thanks for confirmation.

@czardas, no I think the number of parameters will be 0 (parameter list empty) and no unnamed variable will get created at call time. Only inside the callee will one (or more) temp variable(s) be created with its/their default value, due to the difference of the number of parameters declared and the number of arguments actually passed. And I guess that in this case their ByRef attributes will be simply ignored, since it make zero difference.

[czardas]

What you just said reminded me of this song: https://www.youtube.com/watch?v=OFgayzZ5KTM I think it fits the description - from the variable's perspective.

Edited April 20, 2017 by czardas

[GogoTraining]

ByRef parameters are certainly a useful concept but they are not currently available in AutoIt.

[jchd]

@GogoTraining,

Care to reconsider?

[TheDcoder]

1 hour ago, GogoTraining said:

ByRef parameters are certainly a useful concept but they are not currently available in AutoIt.

https://www.autoitscript.com/autoit3/docs/keywords/Func.htm

[GogoTraining]

I expected it to crash or at leas not to compile and run..

[jchd]

It's all about language specifications, not divination, preference, expectation or belief.