This is a wrong D2 program, because the lengths of the arrays don't match:


// Program #1
void main() {
    int[2] a1;
    int[3] a2;
    int[6] result;
    result[] = a1 ~ a2;
}


It compiles with no errors, because a1~a2 produces a dynamic array, despite its length is determined at compile-time. I'd like the compile to catch this bug at compile-time.

The situation in Program #1 is not so common, but a little more refined implementation of the same kind of tests may catch at compile-time more common cases, like:


// Program #2
void main() {
    int[] a1 = new int[2];
    int[] a2 = new int[3];
    int[6] result;
    result[] = a1 ~ a2; // Error
    a1 ~= 0;
    result[] = a1 ~ a2;
}


// Program #3
void main() {
    int[] a1 = new int[2];
    int[] a2 = new int[3];
    int[] result = new int[6];
    result[] = a1 ~ a2; // Error
}