On Wednesday, 12 September 2018 at 14:46:22 UTC, rikki cattermole
wrote:
On 13/09/2018 2:34 AM, drug wrote:
12.09.2018 15:14, Timoses пишет:
On Tuesday, 11 September 2018 at 12:07:14 UTC, drug wrote:
If data size is less or equal to total size of available
registers (that can be used to pass values) than passing by
value is more efficient. Passing data with size less than
register size by reference isn't efficient because you pass
pointer (that has register size) and access memory using it.
Thank you!
So if I pass by reference it will ALWAYS use the address in
memory to fetch the data, whereas passing it by value enables
the (compiler?..) to use the register which has already
loaded the data from memory (stack for example)?
Honestly, I'm not an expert in this domain, but I think so.
Recently used areas of the stack will be available in the cache
in most cases. The issue with passing by reference is it
increases the indirection (number of pointers) that it must go
through to get to the raw bytes.
This is why classes are bad but structs are good. Even if the
struct is allocated on the heap and you're accessing it via a
pointer.
This sounds like classes should never be used.. I don't recall
right now what issues I'm usually encountering with structs that
make me switch to classes (in D).
So passing by reference is generally only applicable (logical) to
structs and non-reference types + only makes sense when the
function being called is supposed to change the referenced value
without returning it.
Except, as Steven pointed out in his post when dealing with large
lvalue structs.
This all seems quite complicated to "get right" when writing
code. I'm sure there are compiler optimizations run on this? Or
is that not possible due to the nature of difference in ref and
value passing.
Anyhow, thanks for the answers! I bet it's possible to write
books on this topic.. Or just mention ones that already were
written : ~D.
