I'm trying to write reference counted dynamic array and
encountered a trouble with compile time reflection at recursive
template instantiation.
for dynamic arrays (and AA too) it is normal to use recursive
declarations:
struct S {
S[] arr;
}
struct S {
Array!S arr;
}
Look at this code: (DPaste - https://dpaste.dzfl.pl/2010191369fe)
import std.string : format;
struct Bar(E) {
void fun() {
pragma(msg, format("fun: Foo.__xdtor - %s",
__traits(hasMember, E, "__xdtor")));
pragma(msg, format("fun: Bar.__xdtor - %s",
__traits(hasMember, Bar, "__xdtor")));
pragma(msg, format("fun: Foo.__dtor - %s",
__traits(hasMember, E, "__dtor")));
pragma(msg, format("fun: Bar.__dtor - %s",
__traits(hasMember, Bar, "__dtor")));
}
~this() {
pragma(msg, format("~this: Foo.__xdtor - %s",
__traits(hasMember, E, "__xdtor")));
pragma(msg, format("~this: Bar.__xdtor - %s",
__traits(hasMember, Bar, "__xdtor")));
pragma(msg, format("~this: Foo.__dtor - %s",
__traits(hasMember, E, "__dtor")));
pragma(msg, format("~this: Bar.__dtor - %s",
__traits(hasMember, Bar, "__dtor")));
}
}
struct Foo {
Bar!Foo foo;
~this() {}
}
void main() {}
Output:
~this: Foo.__dtor - true <--- Foo has __dtor, OK,
~this: Bar.__dtor - true
~this: Foo.__xdtor - false <--- but hasn't __xdtor. WAT???
~this: Bar.__xdtor - true
fun: Foo.__dtor - true
fun: Bar.__dtor - true
fun: Foo.__xdtor - true
fun: Bar.__xdtor - true
Global object.destroy(ref T) function detects destructor presence
by __traits(hasMember, T, "__xdtor")
(https://github.com/dlang/druntime/blob/v2.073.2/src/object.d#L2440) and does nothing in such cases.
Workaround:
Avoid reflection in the destructor. Do reflection in normal
function and then call it from destructor.
But it looks weird and should be fixed.
Also see related topic:
https://forum.dlang.org/thread/[email protected]
