On Monday, 11 February 2013 at 17:15:40 UTC, Maxim Fomin wrote:
On Monday, 11 February 2013 at 06:52:33 UTC, deadalnix wrote:
Ok, We have 2 usages of ref : when you actually need to modify
informations, and for performance reasons. Let's talk about
the second one.
Passing by ref to improve performance is not ideal. First this
is quite hard to know when it is actually faster to pass by
ref and to pass by value, especially in generic code. Secondly
it is easy to forget to use ref at some location, and a lot of
small performance improvement are lost in the process.
Finally, this may be error prone.
I'm thinking about it for a while now and I'm now convinced
that we should allow the compiler to do that job for us. Let
me explain.
When a function accept a struct, the compiler is free to use
that function, or an altered one taking a reference as
parameter. Here are some rules the compiler can use to know
which one to call from callee side :
I expect this to be a nightmare for both users, who would
experience new pile of struct bugs and for developers. How much
code would this proposal break?
None.
What do you mean by 'altered'? Are you taking about two
function versions or a single one? If first, how does it work
with linking, and if second, how does it work for different
situations? What happens when you use function pointer or a
delegate? How __traits works with respect to function type in
case of such optimization? What happens if compiler cannot
deduce from context information required to make such decision?
How does it play with variardic functions? And how such
optimization can be disabled?
The optimization cannot be used on opaques calls. This include
function pointer and alike. The only function that is guaranteed
to exist is the one that take the struct by value. The other one
is an option that the compiler is allowed to choose to make
things faster.
It is applicable for variadic function for non variadic argument,
not for variadic arguments.
Finally, why would you disable something that make your code
faster ?
