On 2011-01-21 04:02, Andrei Alexandrescu wrote:
On 1/20/11 7:18 PM, Luke J. West wrote:
Hi to all from a total noob.
first of all, I'd like to say how impressed I am with D. In fact, I keep
pinching myself. Have I *really* found a language worth leaving C++ for
after two decades? It's beginning to look that way. Obviously I'm
devouring the 2.0 documentation right now, but have not yet found out
how to create a new instance of an existing class object. What I mean
is, given...
auto a = new A;
how do I, in c++ speak, do the D for...
A b(a); // or if you prefer...
A* b = new A(a);
I'm sure this must be trivial.
Many many thanks,
Luke
Hopefully this won't mark a demise of your newfound interest :o). If A
were a struct, auto b = new A(*a) would do. For classes, D does not
provide automatic copy constructors; you need to define and follow a
sort of cloning protocol.
That being said, it's not difficult to define a generic function that
copies fields over from one class object to another. Here's a start:
import std.stdio;
void copyMembers(A)(A src, A tgt) if (is(A == class)) {
foreach (e; __traits(allMembers, A)) {
static if (!is(typeof(__traits(getMember, src, e)) == function)
&& e != "Monitor")
{
__traits(getMember, tgt, e) = __traits(getMember, src, e);
}
}
}
class A {
int x = 42;
string y = "hello";
final void fun1() {}
void fun2() {}
static void fun3(){}
}
void main() {
auto a = new A;
a.x = 43;
auto b = new A;
copyMembers(a, b);
assert(b.x == 43);
}
I think copyMembers belongs to the standard library. I wanted to define
a family of functions like it but never got around to it.
Andrei
Or you can use a serialization library, serialize the struct, then
deserialize it and you have a deep copy. For example using Orange:
http://dsource.org/projects/orange/ . Although it would not be very
efficient to use XML as an intermediate format.
--
/Jacob Carlborg
