In the last line sort calling without "ss" (SwapStrategy) - it is looks like always unstable:
module std.algorithm;
void schwartzSort(alias transform, alias less = "a < b",
SwapStrategy ss = SwapStrategy.unstable, Range)(Range r)
if (isRandomAccessRange!(Range) && hasLength!(Range))
{
alias typeof(transform(r.front)) XformType;
auto xform = new XformType[r.length];
foreach (i, e; r)
{
xform[i] = transform(e);
}
auto z = zip(xform, r);
alias typeof(z.front()) ProxyType;
bool myLess(ProxyType a, ProxyType b)
{
return binaryFun!(less)(a.at!(0), b.at!(0));
}
sort!(myLess)(z); /// <-------------
}