This could should error stating that `a~b` is not allowed in betterC

string foo()()
{
    string a, b;
    return a ~ b;
}
                                                                                                                        
extern(C) void main()
{
    foo();
}

However, it gives a linker error because the compiler chooses to simply not emit the functions that use the GC when using the -betterC switch.