Re: [Vala] [Async] why use .begin ?

[JM <interflug1 gmx net>]

Ok. Thanks!

PS.: Can someone who knows the async stuff better than me write a few
lines about .begin and .end to the vala tutorial?

Regards,
Jörn

Am Freitag, den 18.09.2009, 18:34 +0200 schrieb Michael 'Mickey' Lauer:
> On Friday 18 September 2009 18:18:33 JM wrote:
> > Hi all
> > A few days ago I edited the asynchronous stream reading example on the
> > vala site to use the new async syntax.
> > http://live.gnome.org/Vala/GIOSamples#head-a6170c01121b9fe5825f431de73573b0
> > 84545741
> >
> > After the release of vala-0.7.6 I realized that other examples of the
> > new syntax use '.begin()' to call the async function.
> > I compiled the example with and without the .begin keyword and found NO
> > DIFFERENCE in the generated C code. Both ways are working properly.
> >
> > Is there a case where the difference will be more clear?
>
> Right now I think they're equal, although my view is that it should make a 
> difference when calling an async function from a synchronous one. The principle 
> of least surprise should be that begin() and end() would be collapsed to one 
> synchronous call in that particular case.
>
> Right now async has a related problem though for async methods that return 
> values, i.e. the following code:
>
> ================
> async int func()
> {
>         return 10;
> }
>
> void main()
> {
>         int i = func();
> }
> ================
>
> leads to the -- somewhat surprising -- error message:
>
> ================
> mickey andromeda:/local/pkg/vala/test$ valac --pkg gio-2.0 foo.vala
> foo.vala:8.10-8.15: error: invocation of void method not allowed as expression
>       int i = func();
>               ^^^^^^
> ================
>
> since internally the invocation is moved to func.begin(), which is (always) a 
> void method. This is no problem from async to async as we would be using int i 
> = yield func() in that case, however it's quite common to call async() from 
> sync(), hence some additional work is required here.
>
> :M:
>
> :M:
>
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