2 problems I can't get my head around

[monarch_dodra]

On Monday, 26 November 2012 at 13:08:57 UTC, Manu wrote:
> On 26 November 2012 15:00, monarch_dodra 
> <monarchdodra at gmail.com> wrote:
>
>> On Monday, 26 November 2012 at 12:46:10 UTC, Manu wrote:
>>
>>> On 26 November 2012 14:39, Andrej Mitrovic 
>>> <andrej.mitrovich at gmail.com>**
>>> wrote:
>>>
>>>  On 11/26/12, Manu <turkeyman at gmail.com> wrote:
>>>> > 1.
>>>> >
>>>> > enum i = 10;
>>>> > pragma(msg, is(i == enum) || is(typeof(i) == enum)); // <-
>>>> > > false?!
>>>> >
>>>> > I can't find a way to identify that i is an enum, not a > 
>>>> > variable;
>>>> can not
>>>> > be assigned, has no address, etc.
>>>>
>>>> It's not an enum, it's a manifest constant.
>>>>
>>>>
>>> Well that's certainly not intuitive. I've never even heard 
>>> that term
>>> before. It looks awfully like an enum, with the whole 'enum' 
>>> keyword and
>>> all ;)
>>> How do I detect that then?
>>>
>>
>> The term enum (AFAIK) is comes from an old C++ hack, where 
>> you'd create an
>> actual enum to represent variable that's useable compile-time.
>>
>> Anyways, when you declare an actual enumerate, you have to 
>> declare:
>> 1) The enum type
>> 2) The enum values
>> 3) The enum variable
>>
>> So in your case, it would have to be:
>> --------
>> enum Enumerate
>> {
>>    state1 = 10,
>>    state2
>> }
>> Enumerate i = Enumerate.state1;
>> -----
>>
>
> I'm not looking for a hot-to use enums, I need to know how to 
> form an
> expression to make the pragma show true in precisely that 
> context.

Is see, but (unfortunatly), as already mentioned, the keyword 
"enum" is also used to create a manifest constant. That means the 
tests you are giving your i are irrelevant.

If you really want to test a manifest constant, then I guess you 
can test for the "lvalue-ness" of your variable:
     enum i = 10;
     int j = 10;
     pragma(msg, __traits(compiles, (ref typeof(i) x) { } (i)));
     pragma(msg, __traits(compiles, (ref typeof(j) x) { } (j)));

of the "Compile time knowability"
     enum i = 10;
     int j = 10;
     pragma(msg, __traits(compiles, () {int[i] a;}));
     pragma(msg, __traits(compiles, () {int[j] a;}));

That said, it is not an "iff" relation. I do not know of any way 
to test if something is *only* a manifest constant...