On 12/11/12 9:37 AM, Dan wrote:
On Tuesday, 11 December 2012 at 13:01:44 UTC, Andrei Alexandrescu wrote:
Walter and I discussed that it should be possible to automate the
dupIfNeeded() (I call it ensureUnique()) calls like this:
* If a method is const or immutable, leave as is
* For all other methods, insert a ensureUnique() automatically in the
prolog code
For this to work, the state must be private and all primitives must be
implemented via methods (as opposed to free functions).
This sounds good. But ensureUnique replacing dupIfNeeded really does two
things - (1) determine if a copy is necessary (i.e. has a copy already
been done) and (2) actually do the copy when necessary. What would it
use to do the generic copy and what type of copy would it be (1 level
deep (e.g. dup all fields of typeof(this)) or dup recursively deep)?
That would be left to the user in the form of a .dup primitive.
Automation is only concerned with maintaining the refcount and making
sure duplication is invoked when needed.
I don't think the compiler can choose which of these two is desired by
the user. This would then call for some form of field copy mechanism
similar to postblit, likely defined by user.
I think giving the struct designer a simpler way to do COW sounds very
useful. Would love to read a DIP or notes on it. IMHO there are many
coding use cases for me where even thinking about COW is premature
optimization. For instance, when it comes to configuring a server at
startup I really don't care too much about extra data copies.
Absolutely. On the other hand there's clearly a category of useful
applications. I'll mull over a DIP.
Andrei
