How to specity a list of fields with default to a mixin template?

[realhet]

Hello,

```d
mixin template T(string def, alias C = typeof(mixin("new 
class{"~def~"}")))
{
     enum generatedStr = FieldTypeTuple!C.stringof;
}

void main()
{
     {
     	mixin T!"int a, b;";
         pragma(msg, generatedStr);  //works
     }
     {
	    struct LocalStruct(){ int aaa; }
         mixin T!"LocalStruct ls;";  //can't see localStruct
     	pragma(msg, generatedStr);
     }
}
```

Is there a way to capture local scope in templates?

I've tried to put the expansion of the field declaration into the 
template parameter list, but it is still can't see my local types.

My problem is that I already have a robust Class 
field/constructor/declarator/parent/child/list generator thing, 
and I choosed to specify the list of field declaration by mixing 
in a string into a D construct.  I tried function parameters, and 
now in the example, there is a mixed in anonym class.

But now in whatever modules I want to use my 'Smart" classes I 
have to replicate this same header code to ensure it can see the 
local declarations.

Now it was good for half a year, but today I found out that if a 
module with a generator template uses another module with a 
generator template, the imported module will have 2 generators 
and wil fail.


I would be able to solve this by:
```d
mixin genFields!(AliasSeq!(int, string), ["field1", "field2"], 
AliasSeq!(5, "str"/+default values+/));
```
But this is not so nice.

This is the nice form:
```d
mixin genFields!"int field1=5; string field2=`str`;";
```

But I unable to find a way to parse this declaration in the scope 
where my types are.
I have to copy the genFields template into whatever module I want 
to use it, and I must be careful not to import 2 or more 
genFields to the same scope.

Anyone have an idea?