On Saturday, 3 October 2020 at 23:47:32 UTC, Max Haughton wrote:
The guiding principle to your function parameters should be
correctness - if I am passing a big struct around, if I want to
take ownership of it I probably want to take it by value but if
I want to modify it I should take it by reference (or by
pointer but don't overcomplicate, notice in the previous
example they lower to the same thing). If I just want to look
at it, it should be taken by const ref if possible (D const
isn't the same as C++ const, this may catch you out).
Const-correctness is a rule to live by especially with an big
unwieldy struct.
I would avoid the new in for now, but I would go with const ref
from what you've described so far.
I mostly really only want a read-only view of the struct, and
whether a copy was done or not is academic. However, profiling
showed (what I interpret as) a lot of copying being done in
release builds specifically.
https://i.imgur.com/JJzh4Zc.jpg
Naturally a situation where I need ref I'd use ref, and in the
rare cases where it actually helps to have a mutable copy
directly I take it mutable. But if I understand what you're
saying, and ignoring --preview=in, you'd recommend I use const
ref where I would otherwise use const?
Is there some criteria I can go by when making this decision, or
does it always reduce to looking at the disassembly?
