Templates, D way

[crimaniak via Digitalmars-d]

On Tuesday, 5 September 2017 at 14:55:21 UTC, Void-995 wrote:

> Using unions? <Type>Count and <Type>Offset are different 
> depending on input data, so the address where they are is 
> varying depending on which file I've loaded. Or I didn't get 
> what you meant.
  Yes, so you need separate union type for every type of input 
data. But these values are known in compile time, so you can do 
mixin, creating the union for each type like this:

union MyBinaryStructA
{
     ubyte[...] asBytes;
     struct asStruct
     {
         align(1):
         ubyte[...] dummy1; // padding before firstList
         MyBinarySubStructAForA[...] firstList;
         ubyte[...] dummy2; // padding between lists
         MyBinarySubStructBForA[...] secondList;
         ...
     }
}

unittest
{
     MyBinaryStructA a;

     a.asBytes = someBinarySourceForA; // fill from unstructured 
source

     auto item = a.asStruct.firstList[1]; // access to structure 
element
}