In dmd 2.066beta1 this compiles and works correctly:

void main() pure nothrow @safe @nogc {
    import std.algorithm: sort;
    import std.math: abs;
    int[3] data = [-2, 1, 3];
    auto r = data[].sort!q{a.abs < b.abs};
}



But schwartzSort doesn't support each of those tags:


void main() pure nothrow @safe @nogc {
    import std.algorithm: schwartzSort;
    import std.math: abs;
    int[3] data = [-2, 1, 3];
    auto r = data[].schwartzSort!abs;
}


temp.d(5,20): Error: pure function 'D main' cannot call impure function 'std.algorithm.schwartzSort!(abs, "a < b", cast(SwapStrategy)0, int[]).schwartzSort'
temp.d(5,20): Error: safe function 'D main' cannot call system function 'std.algorithm.schwartzSort!(abs, "a < b", cast(SwapStrategy)0, int[]).schwartzSort'
temp.d(5,20): Error: @nogc function 'D main' cannot call non-@nogc function 'std.algorithm.schwartzSort!(abs, "a < b", cast(SwapStrategy)0, int[]).schwartzSort'
temp.d(5,20): Error: 'std.algorithm.schwartzSort!(abs, "a < b", cast(SwapStrategy)0, int[]).schwartzSort' is not nothrow
temp.d(1,6): Error: function 'D main' is nothrow yet may throw


A schwartzSort has to allocate the mapped items, so perhaps it can't be @nogc (unless you allocate them on the C heap), but I think it can support the other tags.