Andrei Alexandrescu <seewebsiteforem...@erdani.org> wrote:
I do something similar with RefCounted. There are problems - you need to
know in advance which functions you can implement on a null container
(empty and length are obvious candidates, but there could be others).
Static functions can safely be called. Hence, this template:
import std.traits;
template isStaticFunc(T, string fn) {
enum isStaticFunc = is(typeof({
mixin("alias T."~fn~" func;");
ParameterTypeTuple!func args;
mixin("T."~fn~"(args);");
}));
}
Now, Ref can look like this:
struct Ref(Impl) {
private Impl* _impl;
@property ref Impl impl() {
return *(_impl = (_impl ? _impl : new Impl));
}
//alias impl this; // Apparently, alias this takes precedence over
opDispatch, so
// using both doesn't work. Well, unless you put
opDispatch in Impl.
auto opDispatch(string name, T...)(T args) if ( isStaticFunc!(Impl,
name)) {
mixin("return impl."~name~"(_impl,args);");
}
}
struct ExampleImpl {
static int length(ExampleImpl* that) {
return that ? that.actualLength : 0;
}
int actualLength( ) {
return 42;
}
}
import std.stdio;
void main( ) {
Ref!ExampleImpl a;
writeln( a.length );
}
--
Simen
