[Template] Mixins and foreach

[Nicholas Wilson]

On Sunday, 1 October 2017 at 02:29:57 UTC, Jonathan M Davis wrote:
> I would have thought that it would be pretty straightforward to 
> just write a recursive, eponymous template to solve the problem 
> and have it recursively build a single string to mix in for 
> everything.
>
> In general though, without static foreach, you're either going 
> to be using templates to operate in a functional manner rather 
> than a procedural one, or you're going to be writing procedural 
> code that generates a string to mix in. The latter doesn't 
> really work though when the arguments are an AliasSeq of fields 
> like you get from tupleof.
>
> This looks like it would be pretty straightforward to do with a 
> recursive template though.
>
> - Jonathan M Davis

I think I've almost got it:

string generateGetInfo( /*alias*/ Info,alias func,args...)()
{
     string code;
     foreach(field; AliasSeq!(Info.tupleof))
     {
         code ~= "@property " ~ typeof(field).stringof ~ " " ~ 
field.stringof ~ "()" ~
                 "{ " ~
                 "    typeof(return) ret;" ~
                 func.stringof ~ "(" ~ args.stringof ~ "," ~ 
__traits(getAttributes, field).stringof ~ 
",ret.sizeof,&ret,null);" ~
                 "return ret; " ~
                 "}";
         }
     }
     return code;
}
struct MyType
{
     void* raw;
     static struct Info
     {
         @(42) int foo;
     }
     mixin(generateGetInfo!(Info,MyTypeGetInfo,raw));//errors out
     pragma(msg,generateGetInfo!(Info,MyTypeGetInfo,raw)); // also 
errors out
}
but this gives a bunch of

     Error: need 'this' for 'foo' of type 'int'.

even with the pragma msg.
I dont see why though:
     a) the Info struct is static
     b) I'm only using .stringof on the _type's_ fields
     c) its got the name in the errors message! it just wont let 
me use it.

> The latter doesn't really work though when the arguments are an 
> AliasSeq of fields like you get from tupleof.

Why is that and is that what is causing the problem here?

Thanks
Nic