• Liam McSherry (5/5) Jul 27 2016 Since it isn't mentioned in the documentation, do
• Meta (9/15) Jul 27 2016 I think you should be safe here as Fields is basically a wrapper
• Jonathan M Davis via Digitalmars-d (8/13) Jul 27 2016 It's not guaranteed, but given their implementations and what they do, i...

Liam McSherry <mcsherry.liam gmail.com> writes:

Since it isn't mentioned in the documentation, do 
`std.traits.Fields(T)` and `std.traits.FieldNameTuple(T)` return 
the fields and field names in a deterministic order?

Further, will they return the fields/field names in the same 
order? That is, will `fields[0]` be the type of `field_names[0]`?

Meta <jared771 gmail.com> writes:

On Wednesday, 27 July 2016 at 13:09:07 UTC, Liam McSherry wrote:
 Since it isn't mentioned in the documentation, do 
 `std.traits.Fields(T)` and `std.traits.FieldNameTuple(T)` 
 return the fields and field names in a deterministic order?

 Further, will they return the fields/field names in the same 
 order? That is, will `fields[0]` be the type of 
 `field_names[0]`?

I think you should be safe here as Fields is basically a wrapper 
around T.tupleof, which should always return fields in the same 
order. It's not guaranteed anywhere, but it's highly unlikely to 
change.

Since FieldNameTuple is also implemented using T.tupleof, you 
*can* expect Fields!T[0] to be the type of FieldNameTuple!T[0]. 
Again, however, this is an implementation detail that is unlikely 
to change but is not guaranteed.

Jonathan M Davis via Digitalmars-d <digitalmars-d puremagic.com> writes:

On Wednesday, July 27, 2016 13:09:07 Liam McSherry via Digitalmars-d wrote:
 Since it isn't mentioned in the documentation, do
 `std.traits.Fields(T)` and `std.traits.FieldNameTuple(T)` return
 the fields and field names in a deterministic order?

 Further, will they return the fields/field names in the same
 order? That is, will `fields[0]` be the type of `field_names[0]`?

It's not guaranteed, but given their implementations and what they do, it
will almost certainly always be true. But given that it's not guaranteed,
I'm not sure that it would be a great idea to rely on it.

However, there's really no point in relying on it. Just use Fields and use
stringof on a field when you want its name. That's all that FieldNameTuple
is really doing internally anyway.

- Jonathan M Davis