On 08/18/2010 06:46 AM, Vladimir Panteleev wrote:
On Wed, 18 Aug 2010 13:13:25 +0300, Andrei Alexandrescu
<seewebsiteforem...@erdani.org> wrote:
http://www.informit.com/articles/article.aspx?p=1622265
Thanks, that was an interesting read.
It's possible that I'm missing something, but I think that C++'s default
constructors + reference-type structs/classes allow a pattern which
isn't easily translatable to D. For example, in C++...
class A { /* a class with a default constructor */ };
struct B { A a; /* ... */ };
struct C { B b; /* ... */ };
Now, instantiating C will invoke A's constructors. In order for this to
work, the compiler automatically generates hidden constructors for B and
C. However, D doesn't have default constructors for structs (and,
according to TDPL, never will)? D does seem to generate hidden postblit
constructors and destructors, though.
Don't forget that non-default constructors are fair game though. I agree
that for this idiom it would be nice to have the default constructor
guarantee execution of certain initializations.
If I had to port a C++ project to D which made heavy use of this
pattern, what would be the best way to do it? The only ways I see is
either rewriting the code to use classes (which means writing
constructors with explicit instantiation, more dereferences and heap
usage leading to worse performance...), or implementing and calling
pseudo-constructors in both B and C, and (most importantly) all places
which "instantiate" C. Did I miss anything?
One simple technique I use is to write and use factory functions. They
are particularly handy when C is also a template struct.
Andrei
