[foreign-memaccess] on layout equality

[Maurizio Cimadamore]

Hi,
there is one aspect of the layout API that we have not explored fully: 
how should layout behave w.r.t. equality? There are the following options:

1) equality should only test 'core' properties of the layout (e.g. size, 
alignment, ...)
2) equality should also include optional, side-channel info such as 
layout names (or, in the foreign-abi branch, layout annotations)
3) we should have both flavors of equality
4) do not support equality at all

Between (1) and (2), I think I lean towards (1). Yes, we can attach a 
name to a layout, but doing so does NOT change the layout properties - 
the layout still has same size, alignment, etc. On the other hand, (3) 
seems like overkill and (4) seems overly punitive. I say "seem" because 
I really don't know here how people will be using layouts, and it is 
very possible that we are jumping to the conclusion that layouts must 
somehow be comparable with equals() because our implementation internals 
is happy this way. As Brian pointed out once, it is very likely that 
layouts will be constructed, stashed in a static field and never looked 
at again. In which case an answer like (4) is not totally out of the 
question.

What do people think on this?

Cheers
Maurizio