Associative arrays give compile error

[Denis Koroskin]

On Tue, 05 Oct 2010 17:00:13 +0400, Bob Cowdery <bob at bobcowdery.plus.com>  
wrote:

>  On 05/10/2010 13:45, Denis Koroskin wrote:
>> On Tue, 05 Oct 2010 16:32:14 +0400, Bob Cowdery
>> <bob at bobcowdery.plus.com> wrote:
>>
>>>  On 05/10/2010 13:05, Denis Koroskin wrote:
>>>> On Tue, 05 Oct 2010 15:53:55 +0400, Denis Koroskin <2korden at gmail.com>
>>>> wrote:
>>>>
>>>>> 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.
>>>>
>>>> See my other reply for a better solution.
>>>
>>> Thanks very much. It compiles now. The reason I thought it was an issue
>>> was because sometime it did compile a global associative array. I need
>>> to do some homework on what 'this' does. It's clearly a powerful  
>>> concept
>>> and has wider application than class constructors.
>>>
>>
>> "static this" is called a static constructor and can be used for
>> classes and modules. The code in static constructor is guarantied to
>> be called before you use that class/module, it usually happens upon
>> thread initialization.
>>
>> The other solution is better though:
>>
>> enum A_RX_FILT = [                // just works
>>      "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)
>> ];
> I'm not totally understanding that. Why can enum compute that at compile
> time and the thing which it is, an associative array cannot. Is it to do
> with where these things live.

Let's say it's a limitation of dmd compiler. I'll submit a bug report.