This is one example from Phobos, a small part of std.bitmanip.BitArray:


    void init(void[] v, size_t numbits)
    in
    {
        assert(numbits <= v.length * 8);
        assert((v.length & 3) == 0);
    }
    body
    {
        ptr = cast(uint*)v.ptr;
        len = numbits;
    }



But if you compile (with no compilation arguments but the file name) this wrong program runs, with no runtime errors:


import std.bitmanip: BitArray;
void main() {
    ubyte[4] data;
    BitArray bits;
    bits.init(data, 100);
}


The problem is real, but I don't know if the following suggestion is stupid or impossible. 

The idea is to have two precompiled libs, like phobos.lib and phobos_debug.lib (where the debug one contains the asserts too), and DMD (or rmdm) may pick phobos.lib if the -release switch is used, and use phobos_debug.lib otherwise. This may allow to replace the enforce() in Phobos with normal asserts inside DbC contracts.