On 09/07/2011 08:50 PM, Johannes Totz wrote:
On 06/09/2011 12:00, bearophile wrote:
malio:
Okay, thanks bearophile. But I currently doesn't exactly understand
what's the difference between "ref" and "const ref"/"immutable
ref". If "ref" is syntactic sugar for pointers only (like your
first example), does it also create a copy of the parameters which
are marked as "ref"? I thought that pointers (and in this context
also "ref") avoid the creation of costly copies?!?
"ref" just passes a reference to something, so it doesn't perform
copies.
"const ref" or "immutable ref" just means that you can't change the
value (with the usual semantic differences between const and
immutable, that are both transitive).
So if a parameter is immutable (without ref) the compiler could infer a
ref to avoid copy because it can't be modified?
In theory it could. I don't think the current D compilers do that. To
allow it, clear rules would have to be fixed when to apply the
optimization and when not to apply the optimization.
(that is not an issue if the compiler compiles the whole project in one
pass though.)
But probably having to write 'ref' yourself to make calls faster is good
enough, it also does not influence inline assembly in strange and
non-visible ways.
For the programmer that reads your code, "ref" means the function you
have written will usually modify the given argument, while "const
ref" means it will not modify it.
