Re: [Vala] Using uninitialized Glib.TimeVal

[Alexander Krivács Schrøder]

On 14.04.2013 23:09, Evan Nemerson wrote:
> On Sun, 2013-04-14 at 18:38 +0200, Alexander Krivács Schrøder wrote:
>> Hi.
>>
>> I'm trying to use Glib.TimeVal with its from_iso8601() initializer, but
>> I can't get the generated C code not to contain a call to
>> g_get_current_time() first. At first, I tried this Vala code:
>>
>> string iso8601_date = "1999-05-31T11:20:00";
>> TimeVal time_val;
>> time_val.from_iso8601(iso8601_date);
>>
>> but that makes the compiler complain:
>>
>> error: use of possibly unassigned local variable `time_val'
>>
>> So then I tried this code:
>>
>> string iso8601_date = "1999-05-31T11:20:00";
>> TimeVal time_val = TimeVal();
>> time_val.from_iso8601(iso8601_date);
>>
>> but that makes the compiler output the following code:
>>
>> g_get_current_time (&time_val);
>> g_time_val_from_iso8601 (iso8601_date, &time_val);
>>
>> What do I do to make it not call g_get_current_time()? I know it's
>> probably minimal, but it's still wasted CPU cycles and extraneous code
>> to compile and whatnot, and I want the option to leave it out if at all
>> possible. If it isn't possible, a way to make it possible should be
>> considered to be implemented.
> TimeVal time_val = {};
> time_val.from_iso8601 (iso8601_date);
>
>
> -Evan
>
Thank you, that did the trick. :) Exactly the behavior I was looking for
in the C code.

Regards,
Alexander K. Schrøder



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Re: [Vala] Using uninitialized Glib.TimeVal

[Evan Nemerson]

On Sun, 2013-04-14 at 18:38 +0200, Alexander Krivács Schrøder wrote:
> Hi.
> 
> I'm trying to use Glib.TimeVal with its from_iso8601() initializer, but
> I can't get the generated C code not to contain a call to
> g_get_current_time() first. At first, I tried this Vala code:
> 
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val;
> time_val.from_iso8601(iso8601_date);
> 
> but that makes the compiler complain:
> 
> error: use of possibly unassigned local variable `time_val'
> 
> So then I tried this code:
> 
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val = TimeVal();
> time_val.from_iso8601(iso8601_date);
> 
> but that makes the compiler output the following code:
> 
> g_get_current_time (&time_val);
> g_time_val_from_iso8601 (iso8601_date, &time_val);
> 
> What do I do to make it not call g_get_current_time()? I know it's
> probably minimal, but it's still wasted CPU cycles and extraneous code
> to compile and whatnot, and I want the option to leave it out if at all
> possible. If it isn't possible, a way to make it possible should be
> considered to be implemented.

TimeVal time_val = {};
time_val.from_iso8601 (iso8601_date);


-Evan

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Re: [Vala] Using uninitialized Glib.TimeVal

[Alexander Krivács Schrøder]

On 14.04.2013 21:31, Jonas Kulla wrote:
> 2013/4/14 Alexander Krivács Schrøder  >
>
> Hi.
>
> I'm trying to use Glib.TimeVal with its from_iso8601()
> initializer, but
> I can't get the generated C code not to contain a call to
> g_get_current_time() first. At first, I tried this Vala code:
>
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val;
> time_val.from_iso8601(iso8601_date);
>
> but that makes the compiler complain:
>
> error: use of possibly unassigned local variable `time_val'
>
> So then I tried this code:
>
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val = TimeVal();
> time_val.from_iso8601(iso8601_date);
>
> but that makes the compiler output the following code:
>
> g_get_current_time (&time_val);
> g_time_val_from_iso8601 (iso8601_date, &time_val);
>
> What do I do to make it not call g_get_current_time()? I know it's
> probably minimal, but it's still wasted CPU cycles and extraneous code
> to compile and whatnot, and I want the option to leave it out if
> at all
> possible. If it isn't possible, a way to make it possible should be
> considered to be implemented.
>
> Regards,
> Alexander K. Schrøder
>
>
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>
>
> Hi,
>
> GTimeVal seems a little bit problematic. Ideally, you would want to
> declare
> the "from_iso8601" method as a named constructor to circumvent the default
> one (which results in the g_get_current_time), and from a small test I
> just did
> this works out fine Vala wise. The only problem I see is that this
> call returns
> a boolean indicating whether the conversion was successful, which would be
> lost without any way to find out the result. I guess the way it should
> really be
> done is to have the default constructor just initialize the struct to
> zero and have
> the "get_current_time" as a separate method, but for that additional
> glib code
> would have to exist.
>
> I think your best trade off would be to go with your first suggestion
> and ignore
> the valac warning. But why is circumventing the get_current_time call so
> important to you? Are you running this code in a tight loop?
>
> Jonas

I would go with my first suggestion, except it's an error and not a
warning, so it doesn't compile at all.

No, I don't particularly need to circumvent the call. This is mostly a
theoretical desire to be able to accomplish in Vala the same thing I
could accomplish in C.

Were I to write the code in C, I could just leave out the call, so why
shouldn't I be able to accomplish the same goal in Vala? Or, more
appropriately, why should Vala HAVE to call g_get_current_time just for
me to get a hold of a TimeVal struct?

For the most part, Vala produces code about as efficient as manual C
code can be written, which is one of the main reasons why I like Vala so
much, but when it decides to force me to throw in a function call that I
don't need, that feeling of efficiency falls a little short.

So yeah... mostly intellectual curiosity, really.

Regards,
Alexander K. Schrøder


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Re: [Vala] Using uninitialized Glib.TimeVal

[Jonas Kulla]

2013/4/14 Alexander Krivács Schrøder 

> Hi.
>
> I'm trying to use Glib.TimeVal with its from_iso8601() initializer, but
> I can't get the generated C code not to contain a call to
> g_get_current_time() first. At first, I tried this Vala code:
>
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val;
> time_val.from_iso8601(iso8601_date);
>
> but that makes the compiler complain:
>
> error: use of possibly unassigned local variable `time_val'
>
> So then I tried this code:
>
> string iso8601_date = "1999-05-31T11:20:00";
> TimeVal time_val = TimeVal();
> time_val.from_iso8601(iso8601_date);
>
> but that makes the compiler output the following code:
>
> g_get_current_time (&time_val);
> g_time_val_from_iso8601 (iso8601_date, &time_val);
>
> What do I do to make it not call g_get_current_time()? I know it's
> probably minimal, but it's still wasted CPU cycles and extraneous code
> to compile and whatnot, and I want the option to leave it out if at all
> possible. If it isn't possible, a way to make it possible should be
> considered to be implemented.
>
> Regards,
> Alexander K. Schrøder
>
>
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>
>
Hi,

GTimeVal seems a little bit problematic. Ideally, you would want to declare
the "from_iso8601" method as a named constructor to circumvent the default
one (which results in the g_get_current_time), and from a small test I just
did
this works out fine Vala wise. The only problem I see is that this call
returns
a boolean indicating whether the conversion was successful, which would be
lost without any way to find out the result. I guess the way it should
really be
done is to have the default constructor just initialize the struct to zero
and have
the "get_current_time" as a separate method, but for that additional glib
code
would have to exist.

I think your best trade off would be to go with your first suggestion and
ignore
the valac warning. But why is circumventing the get_current_time call so
important to you? Are you running this code in a tight loop?

Jonas
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[Vala] Using uninitialized Glib.TimeVal

[Alexander Krivács Schrøder]

Hi.

I'm trying to use Glib.TimeVal with its from_iso8601() initializer, but
I can't get the generated C code not to contain a call to
g_get_current_time() first. At first, I tried this Vala code:

string iso8601_date = "1999-05-31T11:20:00";
TimeVal time_val;
time_val.from_iso8601(iso8601_date);

but that makes the compiler complain:

error: use of possibly unassigned local variable `time_val'

So then I tried this code:

string iso8601_date = "1999-05-31T11:20:00";
TimeVal time_val = TimeVal();
time_val.from_iso8601(iso8601_date);

but that makes the compiler output the following code:

g_get_current_time (&time_val);
g_time_val_from_iso8601 (iso8601_date, &time_val);

What do I do to make it not call g_get_current_time()? I know it's
probably minimal, but it's still wasted CPU cycles and extraneous code
to compile and whatnot, and I want the option to leave it out if at all
possible. If it isn't possible, a way to make it possible should be
considered to be implemented.

Regards,
Alexander K. Schrøder



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