On 2/22/11 1:04 PM, Nick wrote:
Coming from Andrei's work in C++ "Modern C++ Programming" I wonder how
to implement many of those patterns in D?
In C++ I would work with type lists and use lots of multiple inheritance
and templates to get the magic I need.
D lacks MI, classes and delegates seem heavy (allocated on heap, with
one extra pointer and new for each delegate) and has instead template
mixins which do not create types and string mixing which create...
anything.
So I am a bit lost.
I guess I am looking for some code&examples to read to "get" GP in D. A
bit like "Modern C++ Programming".
Of course, the basic question being: is D2 sufficient to support
everything that is possible in C++?
Thanks!
Welcome to the group.
Using D for the kind of generic designs featured in MC++D may be a bit
disconcerting because a lot of the C++ implementation is forced to use
unintuitive mechanisms to get things done. The expectation is that the
same mechanisms need to be used for the D implementation, too, which
shouldn't be the case. In fact accomplishing any of MC++D's tasks is
considerably easier in D.
For example, indeed in C++ a policy-based design would need to use
multiple inheritance. But this is not motivated by a need for multiple
subtyping - MI is just the best proxy C++ has for injecting
parameterized implementation. In D for that goal you'd use mixin
templates, or for ultimate flexibility string mixins. If you do need
multiple subtyping, you'd use classes in conjunction with e.g.
parameterized interfaces and/or "alias this".
Typelists are an elaborate C++ construct that is essentially built in
into D.
For the Command pattern, delegates would be a great start. Added value
for e.g. currying and binding is trivial to implement, to the extent
that we decided to deprecate a dedicated module (std.bind).
There would be more to say. One way or another, policy-based design is
difficult and often unintuitive. Therefore, it requires mastery of both
the design topic at hand and of the implementation language. I think
trying to get a solid PBD component off the ground as a D beginner would
be pushing it. Nevertheless, it may be worth a try. I suggest starting
with a simple, well-defined component such as Object Factory.
Andrei
