import std.stdio;

class Foo {
  int foobar(int a, int b)
  in {
    assert (a > 0 && b > 0);
    writeln("Foo in");
  } out(ret) { 
    assert(ret > 0);
    writeln("Foo out");
  } body {
    return a + b;
  }
}

class Bar : Foo {
  override int foobar(int a, int b)
  in {
    assert(a * b + 8 > 1);
    writeln("Bar in");
  } out(ret) {
    assert (ret > 1);
    writeln("Bar out");
  } body {
    return 2;
  }
}


void main() {
  try {
    auto _foo = new Bar();
    _foo.foobar(1, 2);
  } catch (Exception e) {
    writeln(e);
  }
}


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IN contract for function Bar.foobar() is never checked.
For me it makes sense (becuse in contracts must be checked by the caller which may not know anything about overriding function) but compiler should not allow to define IN contract for an overriding function.