module main;

struct TestStruct
{
    int a;
    int b;
    int c;
}

template getSomeMember(T)
{

    enum allMembers = __traits(allMembers, T);
    enum getSomeMember = allMembers[0];

}

void main(string[] args)
{

    enum someMember = getSomeMember!TestStruct;

}

Gives me the following erorrs:
main.d(13): Error: variable _allMembers_field_0 cannot be read at compile time
main.d(21): Error: template instance main.getSomeMember!(TestStruct) error instantiating

Running dmd 2.062

On Saturday, 23 March 2013 at 10:46:11 UTC, Martin wrote:
>     enum allMembers = __traits(allMembers, T);

Try:
     enum allMembers = [__traits(allMembers, T)];

On Saturday, 23 March 2013 at 11:55:37 UTC, Andrej Mitrovic wrote:
> On Saturday, 23 March 2013 at 10:46:11 UTC, Martin wrote:
>>    enum allMembers = __traits(allMembers, T);
>
> Try:
>      enum allMembers = [__traits(allMembers, T)];

That actually works, thanks. I thought tuples were supposed be indexable though

On Sat, Mar 23, 2013 at 12:57 PM, Martin <martinbbjerregaard@gmail.com> wrote:
> On Saturday, 23 March 2013 at 11:55:37 UTC, Andrej Mitrovic wrote:
>>
>> On Saturday, 23 March 2013 at 10:46:11 UTC, Martin wrote:
>>>
>>>    enum allMembers = __traits(allMembers, T);
>>
>>
>> Try:
>>      enum allMembers = [__traits(allMembers, T)];
>
>
> That actually works, thanks. I thought tuples were supposed be indexable though

They are, I think it's a bug.

If the alias grammar was more open, we could do:

alias allMembers = __traits(allMembers, T);

but since __traits are not accepted as an alias target, we must use a wrapping template as a workaround:

import std.stdio;

struct TestStruct
{
    int a;
    int b;
    int c;
}

/// Just to hide __traits:
template Alias(aliases...)
{
    alias Alias = aliases;
}

template getSomeMember(T)
{

    alias members = Alias!(__traits(allMembers, T));

    // now members is a tuple of members
    // perfectly indexable & slicable
    enum getSomeMember = allMembers[0];

}

void main(string[] args)
{
    enum someMember = getSomeMember!TestStruct;
    writeln(typeof(someMember).stringof);
    writeln(someMember);
}

On Saturday, 23 March 2013 at 12:12:30 UTC, Philippe Sigaud wrote:
> On Sat, Mar 23, 2013 at 12:57 PM, Martin <martinbbjerregaard@gmail.com> wrote:
>> On Saturday, 23 March 2013 at 11:55:37 UTC, Andrej Mitrovic wrote:
>>>
>>> On Saturday, 23 March 2013 at 10:46:11 UTC, Martin wrote:
>>>>
>>>>    enum allMembers = __traits(allMembers, T);
>>>
>>>
>>> Try:
>>>      enum allMembers = [__traits(allMembers, T)];
>>
>>
>> That actually works, thanks. I thought tuples were supposed be indexable
>> though
>
> They are, I think it's a bug.
>
> If the alias grammar was more open, we could do:
>
> alias allMembers = __traits(allMembers, T);
>
> but since __traits are not accepted as an alias target, we must use a
> wrapping template as a workaround:
>
> import std.stdio;
>
> struct TestStruct
> {
>     int a;
>     int b;
>     int c;
> }
>
> /// Just to hide __traits:
> template Alias(aliases...)
> {
>     alias Alias = aliases;
> }
>
> template getSomeMember(T)
> {
>
>     alias members = Alias!(__traits(allMembers, T));
>
>     // now members is a tuple of members
>     // perfectly indexable & slicable
>     enum getSomeMember = allMembers[0];
>
> }
>
> void main(string[] args)
> {
>     enum someMember = getSomeMember!TestStruct;
>     writeln(typeof(someMember).stringof);
>     writeln(someMember);
> }

I see, thanks a lot