On Friday, 27 April 2012 at 16:02:00 UTC, Steven Schveighoffer
wrote:
On Fri, 27 Apr 2012 11:33:39 -0400, Joseph Rushton Wakeling
On 27/04/12 17:18, Steven Schveighoffer wrote:
const should not affect code generation *at all*, except for
name mangling
(const MyStruct is a different type from MyStruct), and
generating an extra
TypeInfo for const MyStruct and const MyStruct[]. Const is
purely a compile-time
concept.
This cannot account for an extra 2 seconds. Something else is
happening.
The code is here: https://github.com/WebDrake/Dregs/
You'll see that there are about 8 different functions in there
which receive as input an array of type Rating!(UserID,
ObjectID, Reputation)[]. These were the inputs I was marking
as const.
Hm.. you have marked all your functions pure as well. I don't
think this will affect anything in the current implementation,
but it might. However, I'd expect the opposite (const version
is faster) if anything.
Perhaps I'm wrong, but seeing as your working with a struct I
would think the following should be noted.
First, pure and nothrow. Nothing wrong with labeling functions
as such, but I would recommend removing them and once the whole
thing is done and you get it in a finished state that you start
adding them back in if you think they qualify. Recently I know I
added a @safe token to a simple function which of course threw a
range exception later. Oddly enough it was because I didn't check
if the array was null before accessing it.
Second, you are passing an array of structs. Either a fat
pointer is being passed, or it's shallow copying; depending on
the scenario either could be true. As an array it should be
passing a fat pointer but if the compiler has to make certain
guarantees based on your tags it may not. Depending on the size
of the array, I would think this might be the case.
Actually I _think_ it would in this case. Imagine a pure
function that gives different results from the input when the
input changes during execution. By making a local copy the input
can't be changed from the outside and thereby returns that
guarantee.
Last try adding ref after const; At the off chance it's shallow
copying, this should remove that.
