Associative arrays give compile error

[Denis Koroskin]

On Tue, 05 Oct 2010 15:40:39 +0400, Bob Cowdery <bob at bobcowdery.plus.com>  
wrote:

>  On 05/10/2010 12:13, Denis Koroskin wrote:
>> On Tue, 05 Oct 2010 15:08:39 +0400, Bob Cowdery
>> <bob at bobcowdery.plus.com> wrote:
>>
>>>  On 05/10/2010 12:04, Denis Koroskin wrote:
>>>> On Tue, 05 Oct 2010 14:57:22 +0400, Bob Cowdery
>>>> <bob at bobcowdery.plus.com> wrote:
>>>>
>>>>>  On 05/10/2010 11:45, Denis Koroskin wrote:
>>>>>> On Tue, 05 Oct 2010 14:23:47 +0400, Bob Cowdery
>>>>>> <bob at bobcowdery.plus.com> wrote:
>>>>>>
>>>>>>>  I can't seem to get any sense out of associative arrays. Even the
>>>>>>> simplest definition won't compile so I must be doing something  
>>>>>>> daft.
>>>>>>>
>>>>>>> int[string] aa = ["hello":42];
>>>>>>>
>>>>>>> Error: non-constant expression ["hello":42]
>>>>>>>
>>>>>>> What exactly is not constant about this. The example is straight
>>>>>>> out the
>>>>>>> book. Using D 2.0.
>>>>>>>
>>>>>>> bob
>>>>>>
>>>>>> What exactly compiler version are you using (run dmd with no args)?
>>>>>> Works perfectly fine here (dmd2.049).
>>>>>
>>>>> It says 2.049. How odd. I've got a fair amount of code and everything
>>>>> else compiles fine.
>>>>
>>>> Can you please post complete code snippet that fails to compile?
>>>>
>>>> Here is the code I used to test:
>>>>
>>>> module aa;
>>>>
>>>> import std.stdio;
>>>>
>>>> void main()
>>>> {
>>>>     int[string] aa = ["hello":42];
>>>>     writeln(aa["hello"]);
>>>> }
>>>>
>>>> # dmd -run aa.d
>>>
>>> Ah! It's some other code below it that is not giving an error but
>>> causing the error above. So the compiler is getting confused. What I  
>>> was
>>> actually trying to do was create an associative array with a string as  
>>> a
>>> key and a Tuple as the value. Now
>>>
>>> auto aa = [
>>>     "some string": (100.0, 6100.0)
>>> ]
>>>
>>> compiles but is clearly wrong and gives rise to other errors.  Does
>>> anyone know the correct way to define this and then access the tuple.
>>
>> import std.stdio;
>> import std.typecons;
>>
>> void main()
>> {
>>     auto aa = ["hello": tuple(100.0, 6100.0)];
>>     auto result = aa["hello"];
>>
>>     writeln(result.field[0], " ", result._1); // primary and
>> alternative way
>> }
>
> Thanks. I've established that works for me and also that the actual
> array I'm using also works in the test program but it won't compile in
> the real program. I've commented everything else out of the file and
> just left...
>
> import std.typecons;
>
> auto A_RX_FILT = [
>     "6K0": tuple(100.0, 6100.0),
>     "2K4": tuple(300.0, 2700.0),
>     "2K1": tuple(300.0, 2400.0),
>     "1K0": tuple(300.0, 1300.0),
>     "500": tuple(500.0, 1000.0),
>     "250": tuple(600.0, 850.0),
>     "100": tuple(700.0, 800.0)
> ];
>

You are trying to declare global variable and initialize at in compile  
time. As far as I know, you can't initialize AA at compile time atm (this  
might be implemented in future though).

As such, I'd recommend against using global variables (try moving it to  
some class or something). Anyway, you need to initialize it at some point,  
either manually:

Tuple!(double,double)[string] A_RX_FILT;

void init()
{
     A_RX_FILT = [
	"6K0": tuple(100.0, 6100.0),
	"2K4": tuple(300.0, 2700.0),
	"2K1": tuple(300.0, 2400.0),
	"1K0": tuple(300.0, 1300.0),
	"500": tuple(500.0, 1000.0),
	"250": tuple(600.0, 850.0),
	"100": tuple(700.0, 800.0)
     ];
}

or automatically at thread startup:

static this()
{
     init();
}

Hope that helps.