Re: 'academic' problem ( speed/memory efficiency vs. human readability and
SeeWebsiteForEmail@erdani.org (Andrei Alexandrescu (See Website For
Email)) wrote (abridged):
Which is why I generally advocate pass by const reference and make the
copy internally if I need to.
How about nonvirtual (including free) functions? Let's not forget going
the other way is just as short and simple (actually simpler as we
eliminate the copy). I call it premature optimization when time is
spent to implement something that may also become less understandable
in the process. In this case the code makes me feel good
performance-wise at no cost. I do recommend trying it.
Let's say we design the interface for the function before we design its
implementation. So when we are writing the function signature, we don't
know if the body will make a copy. So we make it use a const reference.
Does all this sound reasonable so far?
Now we implement the function body. We discover we do need to make a copy.
As I understand it, you are saying that we should go back and edit the
function signature to use pass-by-copy. To me this is more work,
especially as the function signature will typically be repeated in two
places, one of them a header.
It's not a big deal, obviously, but technically I think it is premature
optimisation. It's doing extra effort for the sake of performance without
profiling data to justify it.
I also think the resulting code is less understandable, but that may be
because I am not used to your convention. Currently whenever I see someone
passing, say, a vector, by value, a mental red-flag goes up. I wonder
whether the author doesn't know how expensive copying a vector can be,
compared to passing a const reference to one. This at best distracts me
from what I am doing. At worst I'll investigate, find the function's
definition and see what it is doing.
This is partly about violating the principle of least surprise, where what
is surprising depends on local conventions. However, your convention does
make it harder to spot where someone has used pass-by-value by mistake. It
is a fairly common mistake for people new to the language. I almost want
every use of pass-by-value to have a documenting comment explaining the
optimisation :-)
-- Dave Harris, Nottingham, UK.
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