struct / cast / ? design problem

[Charles Hixson via Digitalmars-d-learn]

On 03/16/2015 01:24 PM, via Digitalmars-d-learn wrote:
> The problem in your example is that your making a copy of the returned 
> data. Of course any changes to that copy won't affect the original. 
> You need to return a pointer to it (`ref` won't do if you want to 
> store it in a local variable, because these can't be `ref`).
>
> struct BlockHead
> {
>     uint magic = 20150312;
>     uint magic2;
>     uint blockSize;
>     uint unused1;
>     ulong unused2;
>     ulong spare[61];
>
>     T* embedded(T)() {
>         static assert(T.sizeof < spare.length);
>         return cast(T*) spare.ptr;
>     }
> }
>
> How to use it:
>
> void useIt(ref BlockHead bh) {
>     static struct InternalData {
>         int foo;
>         ubyte[20] bar;
>     }
>
>     auto data = bh.embedded!InternalData;
>     data.foo = 42;
> }
>
Nice!  That looks like exactly what I was hoping for.