How to create mixin template and pass name of a variable?

[Andrej Mitrovic]

On Friday, 2 August 2013 at 11:37:27 UTC, Bosak wrote:
> I want to create a mixin template such that:
>
> mixin template ArgNull(alias arg, string name)
> {
>     if(arg is null)
>         throw new Exception(name~" cannot be null.");
> }
>
> But is there a way to do that with only one template argument. 
> And then use it like:
>
> string text = null;
> mixin ArgNull!(text);
>
> And the above mixin to make:
>
> if(text is null)
>     throw new Exception("text cannot be null.");

Note that template mixins cannot inject arbitrary code, they can 
only inject declarations. You can use '__traits(identifier, 
symbol)' on an alias parameter to retrieve the symbol name, for 
example:

-----
mixin template ArgNull(alias arg)
{
     void test()
     {
         if (arg is null)
             throw new Exception(__traits(identifier, arg) ~ " 
cannot be null.");
     }
}

string text = null;
mixin ArgNull!text;

void main()
{
     test();
}
-----