Is there a general philosophy in D phobos on when to pass by
value or
reference? For instance, to find a slice using lowerBound many
copies
of the target item, as well as copies of items in the collection
are
made (see code example below). This seems unnecessary - why not
have
functions like:
auto lowerBound(...)(V value)
be:
auto lowerBound(...)(ref V value)
or:
auto lowerBound(...)(auto ref V value)
Is this a source for desire for no postblits, shallow semantics on
copy/assignment with additional logic for copy on write
semantics. If
libraries in general are coded to make many copies of parameters
it
might be a big improvement to not have postblits. A general
purpose
library accessing ranges will not know the semantics of V (deep or
shallow), so why incur the cost of copies? Certainly finding a
lowerBound on a range of V can be done with 0 copies of elements?
Is there an established philosophy?
Thanks
Dan
-------
struct S {
DateTime date;
double val;
this(this) { writeln("copying S ", &this, ' ', date, ',',
val); }
}
---------------
auto before(ref const(ValueType) vt) const {
auto ass = assumeSorted!orderingPred(_history[]);
writeln("Before lb");
auto lb = ass.lowerBound(vt);
writeln("After lb");
return History!(V, orderingPred)(_history[0 .. lb.length]);
}
---------------
Before lb
copying S 7FFF622CE110 2001-Nov-01 00:00:00,0
copying S 7FFF622CE090 2001-Nov-01 00:00:00,0
copying S 7FFF622CE020 2001-Jan-01 00:00:00,100
copying S 7FFF622CE030 2001-Nov-01 00:00:00,0
copying S 7FFF622CDF90 2001-Jan-01 00:00:00,100
copying S 7FFF622CDFA0 2001-Nov-01 00:00:00,0
copying S 7FFF622CE020 2002-Jan-01 00:00:00,200
copying S 7FFF622CE030 2001-Nov-01 00:00:00,0
copying S 7FFF622CDF90 2002-Jan-01 00:00:00,200
copying S 7FFF622CDFA0 2001-Nov-01 00:00:00,0
copying S 7FFF622CE020 2001-Jan-01 00:00:00,200
copying S 7FFF622CE030 2001-Nov-01 00:00:00,0
copying S 7FFF622CDF90 2001-Jan-01 00:00:00,200
copying S 7FFF622CDFA0 2001-Nov-01 00:00:00,0
After lb
