This is wrong D2 code because Foo has no constructor:


class Foo(T) {
    T x;
    Foo y;
}
auto foo(T)(T x, Foo!T y=null) {
    return new Foo!T(x, y);
}
void bar(U)(U foo, U[] spam=[]) {
    spam ~= [];
}
void main() {
    bar(foo(0));
}



DMD 2.059head gives:

test.d(6): Error: no constructor for Foo
test.d(12): Error: template instance test.foo!(int) error instantiating

Followed by a crash.



If I remove the template of Foo:


class Foo {
    int x;
    Foo y;
}
auto foo(int x, Foo y=null) {
    return new Foo(x, y);
}
void bar(U)(U foo, U[] spam=[]) {
    spam ~= [];
}
void main() {
    bar(foo(0));
}



DMD gives this and no crash:

test.d(6): Error: no constructor for Foo
test.d(12): Error: forward reference to foo