Re: Unicode confusables and reordering characters considered harmful, a simple solution

[Gregory Heytings]

> > > But they don't.  Not more than just using RTL characters within LTR 
> > > text would.  Just revisit the example posted by Stefan (which I 
> > > slightly modified to be more realistic):
> > >
> > >      myfun("שָׁלוֹם" ,"السّلامعليكم");
> > >
> > > Which string does this function call pass as the first argument, and 
> > > which as the second one?
> >
> > There is no danger in that example, and in particular nothing 
> > invisible.
>
> Ha-ha, very funny.

It wasn't supposed to be funny.

> > The programmer must just be aware that compilers read source code files 
> > in byte order, which might be different from the order in which the 
> > string is displayed on screen, but is identical to the order in which 
> > one forward-char's through the string.
>
> If we are going to assume users forward-char through every piece of code 
> they look at, then the examples we were discussing present no problem, 
> either.

I'm not assuming any of this.  There are programmers who read Hebrew and 
Arabic, and those who don't.  Those who do know them know that they are 
entered and read RTL, and don't even need to check the argument order. 
Those who don't may not know this, and can easily check if they have some 
doubt about what string is passed in which argument.

> > There is a danger when, because the source code contains invisible 
> > control characters, the programmer sees something on their screen, and 
> > the compiler sees something completely different.
>
> That's exactly what happens in the above example.  Except that 
> reordering happens automatically without any invisible characters, i.e. 
> also "invisibly".

There are no invisible characters doing weird things with the text, no. 
And it's those invisible characters that the "Trojan Source" paper is 
about.  Not potential interpretation problems by those who would discover 
RTL languages.