Re: [Vala] readline from a FileStream?

[Frederik <scumm_fredo gmx net>]

Dov Grobgeld wrote:
> Building on Frederik's answer, I built myself an iteratable interface to 
> line reading which looks just like python. This is already pretty. :-)
>
> I don't understand how the following works though:
>
>             next_line = fi.dis.read_line (null, null) + "\n";
>             return next_line!=null;
>
> I would rather write it:
>
>             next_line = fi.dis.read_line(null,null);
>             if (next_line != null)
>                 next_line = next_line + "\n"
>
> but that gives me an error of:
>
>             iter.vala:20.29-20.44: error: Arithmetic operation not 
> supported for types `string' and `string'
>                 next_line = next_line + "\n";
>
> why? What's the difference?
>
> Regads,
> Dov

Hi Dov,

it seems to have something to do with generics. I think inside the class
the name "string" is known as a new generic type, not as the original
"string" type, just as if you had written "class Iterator<Y>" instead of
"class Iterator<string>". With a generic type like Y the + operator is
not allowed, because Y could be of any type. I think instead of

  private class Iterator<string> : GLib.Object, Gee.Iterator<string> { 
... }

it should be

  private class Iterator : GLib.Object, Gee.Iterator<string> { ... }

then your string concatenation works fine, and now I would expect the
generic parts of the interface to be fixated on the type "string"
without introducing a new generic type, but unfortunately now the
compiler complains about an incompatible return type for get(). To me
this seems like a Vala bug.


Regards,

Frederik