New abstraction: Layout

[Andrei Alexandrescu]

On 02/17/2018 09:03 AM, Steven Schveighoffer wrote:
> On 2/17/18 8:19 AM, Steven Schveighoffer wrote:
>> On 2/16/18 7:04 PM, Andrei Alexandrescu wrote:
>>> I've been long bothered that the builtin .tupleof and our own 
>>> abstractions Fields and RepresentationTypeTuple in std.traits - all 
>>> omit the essential information of field offsets. That makes types 
>>> that use align() to have the same .tupleof, Fields, and 
>>> RepresentationTypeTuple even though they shouldn't.
>>>
>>> The right answer is Layout a tuple of (offset, type) pairs describing 
>>> entirely the memory layout of a type. We need such for memory 
>>> allocation, garbage collection, serialization, and more.
>>>
>>> The implementation turned out to be quite compact - 81 lines 
>>> including a compile-time mergesort. Destroy!
>>>
>>> https://github.com/dlang/phobos/pull/6192
>>
>> Can't you just use offsetof?
>>
>> struct S
>> {
>>     ubyte x;
>>     int y;
>> }
>>
>> static foreach(i; 0 .. s.tupleof.length)
>> {
>>     writeln(s.tupleof[i].offsetof);
>> }
>>
>> outputs:
>> 0
>> 4
> 
> I found this also works:
> 
> static foreach(alias x; S.tupleof)
> {
>     writeln(x.offsetof);
> }

Yes, the implementation uses offsetof. -- Andrei