How to assign a delegate to a var ?

[bioinfornatics via Digitalmars-d-learn]

On Monday, 2 June 2014 at 23:27:03 UTC, Meta wrote:
> On Monday, 2 June 2014 at 22:18:39 UTC, bioinfornatics wrote:
>> Hi,
>>
>> I would like store the delegate to another var but when i try i
>> get:
>>
>>
>> testTraitsWithDelegate.d(13): Error: expression template
>> __lambda2 is void and has no value
>>
>> I do not want to run it only to save the «function» somewhere.
>>
>>
>> ----------- CODE ------------
>> import std.stdio;
>> import std.typecons : Tuple;
>>
>> struct attribute( alias Pred )
>> {
>>     alias Predicate = Pred;
>> }
>>
>>
>>
>> struct Data
>> {
>>     @attribute!( (a) => a == 42 )
>>     int x;
>> }
>>
>>
>>
>> void main()
>> {
>>
>>     bool delegate( int ) tmp;
>>
>>     pragma( msg, __traits(getAttributes, Data.x)[0].Predicate( 
>> 42
>> ) );
>>
>>     tmp = __traits(getAttributes, Data.x)[0].Predicate;
>> }
>> ----------- END CODE ------------
>
> The problem is that you're missing the type of a in "(a) => a 
> == 42". Without the type, it's actually a template lambda, not 
> a lambda function. Try changing it to "(int a) => a == 42".
> auto

with this i got an error even if i do public alias Predicate in
struct attribute:
Error: struct testTraitsWithDelegate.attribute!(function (int a)
=> a == 42).attribute member __lambda2 is not accessible

and i fail to do same with

struct attribute
{
    public:
      static bool delegate( int ) Predicate;
}