d中的静转,动转

import std.stdio;

@safe:

extern(D) {
    abstract class DA {
        char foo();
    }
    class DB : DA {
        override char foo() { return 'B'; }
    }
    class DC : DA {
        override char foo() { return 'C'; }
    }
}

extern(C++) {
    abstract class CA {
        char foo();
    }
    class CB : CA {
        override char foo() { return 'b'; }
    }
    class CC : CA {
        override char foo() { return 'c'; }
    }
}

void main() {
    DB db = new DB;
    DA da = db;
    DC dc = cast(DC) da;
    writeln((dc is null)? "D cast was dynamic." : "D cast was static.");

    CB cb = new CB;
    CA ca = cb;
    CC cc = cast(CC) ca;
    writeln((cc is null)? "C++ cast was dynamic." : "C++ cast was static.");

    return;
}