// hash.d.  This is part of a library, not the application.  Therefore, it
// is in the import path but is not explicitly passed to DMD
struct HashRange(K, S, ) {
    size_t _length;

    this(S* set) {
        this._length = set.length;
    }

}


struct StackSet(K) {
    
    HashRange!(K, typeof(this)) elems() {
        assert(0);
    }

    
    @property size_t length() {
        assert(0);
    }
}

// a.d.  This is part of the application.
import hash;

// b.d.  This is also part of the application.
import hash;

void fun() {
    StackSet!string alreadyDone;
}

$ dmd -c a.d b.d
hash.d(11): Error: struct hash.StackSet!(string).StackSet no size yet for forward reference
hash.d(5): Error: cannot implicitly convert expression ((*set).length()) of type size_t to ulong
hash.d(13): Error: template instance hash.HashRange!(string,StackSet!(string)) error instantiating
b.d(4):        instantiated from here: StackSet!(string)
b.d(4): Error: template instance hash.StackSet!(string) error instantiating