Re: [Vala] empty List<T> is null - bug or feature?

[Yu Feng <rainwoodman gmail com>]

Filed under Bug #578198 with a patch.


On Tue, 2009-04-07 at 00:27 +0200, Jan Spurny wrote:
> Hi Yu,
>
> thanks for reply - that's exactly what I did in order to get it working now. I know empty list is null in 
> glib, but I'm still a bit troubled by the fact that (as some Java programmer may think):
>
> 1) I've created new object by "var list = new List<Something>;"
> 2) I can call methods on this new object: "var len = list.length();" - which work as anyone would expect
> 3) but when I pass it to some other function it fails (CRITICAL-y!)
>
> Let me explain this - I've "discovered" vala few weeks ago when I was looking something up in gobject 
> documentation and I thought it can be a great tool for our company's libraries (which are then used from 
> Java and maybe Python) as it can dramatically (I still hope..) increase development (and maintenance, I 
> hope..) of some components - the fact is that we have many Java programmers but only few C programmers - so 
> it could allow these Java people to help me in developing these libraries..
> But there are some things, like this empty null glist, a bit complicated (from java/c# programmer's point 
> of view) object construction and "memory management" which requires much deeper knowledge of C and 
> GLib/GType/GObject - don't get me wrong - I do not say that vala is bad language - even if no java 
> programmer will be able to help me soon, it's still a great help for me and my colleagues
>
> BTW: you haven't seen my c programs :) - but I'm definitelly not the best programmer in the world, so can 
> you explain to me if the fact that you havent seen that is because it's not a good programming practice 
> (why?), or it's just that you've never seen it :) ?
>
> Jan Spurny
>
> On Mon, 06 Apr 2009 23:05:16 +0200 (CEST)
> Yu Feng <rainwoodman gmail com> wrote:
>
> > Try List<int>? list
> >
> > In Glib an empty list is by definition null.
> >
> > BTW: I have never seen any of c program passing a GList around.
> >
> > -Yu
> > On Mon, 2009-04-06 at 19:05 +0200, Jan Spurny wrote:
> > > Hi,
> > >
> > > I'd like to know if this is considered to be a bug or feature:
> > > when I pass an empty list to some function/method, it generates critical error - but to any 
> > > Java/C#/C++/Whatever programmer this would be very confusing..
> > > I know the reason for this as I've been working with glib for some time, but those without any previous 
> > > glib experience may be severely confused..
> > >
> > > In case of this being classified as a bug I humbly suggest removing "g_return_if_fail (list != NULL);" 
> > > in generated code as NULL is valid (empty) GLib.List
> > >
> > > here is an example of what I mean:
> > > ---------------------------------------
> > > using GLib;
> > > void print_list(List<int> list) {
> > >     foreach (int x in list)
> > >         stdout.printf("%d\n", x);
> > > }
> > > int main (string[] args) {
> > >     var xy = new List<int>();
> > >     print_list(xy);
> > >     return 0;
> > > }
> > > ----------------------------------------
> > > valac -o list list.vala 
> > > ./list 
> > >
> > > ** (process:6750): CRITICAL **: print_list: assertion `list != NULL' failed
> > > ----------------------------------------
> > >
> > > Thanks in advance for any reply.
> > >
> > > Jan Spurny
> > > _______________________________________________
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