[plt-scheme] cost of closure?

Matthew Flatt wrote:
>    12 = 4 bytes * 3 fields or captured bindings
>     4 = 4 bytes * 1 code (closure) or type (struct) pointer
>     4 = 4 bytes * 1 MzScheme type tag and hash code
>    12 = 12 bytes per cons cell (MzScheme level)
>     8 = 4 bytes * 2 objects for GC's layer of size info
>  ----
>    40

So the cons cell has the same memory footprint as a custom 2 field 
struct? And what about runtime access? How is struct field access 
implemented?

-- 
regards,
Jakub Piotr Cłapa