Built in functions and passing vars by reference

I remember Tomasz had said that if we pass values by reference, built in functions do not work, or give error message. I do not find the documentation where this is explained, after some googling. Is this explained somewhere?

printf gives error message. However NZ() function does not. I setup an example that demonstrates it:

function myFunc( fType )
local ltmp;
    ltmp = fType;
    fType = 26;
    ftype[4] = 30;
    ltmp = fType;
    ftype=Nz(ftype);  // This command messes up the ftype var
    ltmp=Nz(ltmp);  // This command is ok    
    ftype = ltmp;   // a way to fix it
    return true;

    xx1, xx2;

    xx1 = 5; 
    xx1=Nz(xx1);  // This command is ok
    xx2 = myFunc( &xx1 );

For additional info on this topic, see also this thread.

Passing arguments as a reference is still a BETA feature, so the documentation available is only the one that came in the release notes with the beta versions, plus the examples provided by @Tomasz here in the forum.

As any beta feature, IMHO it is better to consider it subject to possible changes in the next stable version.

Thank you very much beppe. This is the thread I had read too.

You can't pass references to built in functions in 6.27.1 yet. As @beppe wrote it is work in progress.