Reduced code (Foo originally was BigInt):


struct Foo {
    bool b = false;
    void opAssign(int x) {
        this.b = true;
    }
}
int foo() {
    Foo[1] array;
    foreach (ref item; array)
        item = 1;
    return 0;
}
enum r = foo(); // error
void main() {
//    const r = foo(); // OK
}


DMD 2.055beta gives:

test.d(9): Error: variable __key4 is used before initialization
test.d(10): Error: cannot evaluate item.opAssign(1) at compile time
test.d(13): Error: cannot evaluate foo() at compile time