The docs explicitly say that SwapStrategy.unstable is non-allocating, but this code (which is for finding the statistical mode of a range) will fail to compile.

auto mode(alias pred = "a == b", R)(R r) @nogc
    if (is(ElementType!R : real) &&
        isInputRange!R &&
        !isInfinite!R)
{
    import core.stdc.stdlib : malloc;

    import std.algorithm.iteration : group;
    import std.algorithm.sorting : sort, SwapStrategy;
    import std.algorithm.mutation : copy;
    import std.typecons : Tuple;

    alias LT = Tuple!(Unqual!(ElementType!R), size_t);

    if (r.empty)
    {
        return real.nan;
    }

    auto grouping = r.group!pred;

    // Because the struct Group does not have swappable elements, it cannot be
    // sorted, so copy it to another array
    auto buffer = (cast(LT*) malloc(r.length * LT.sizeof))[0 .. r.length];
    copy(grouping, buffer);

    sort!("a[1] > b[1]", SwapStrategy.unstable)(buffer);

    return buffer[0][0];
}


$ dmd/src/dmd -unittest test.d
test.d(439): Error: @nogc function 'test.mode!("a == b", int[]).mode' cannot call non-@nogc function 'std.algorithm.sorting.sort!("a[1] > b[1]", cast(SwapStrategy)0, Tuple!(int, ulong)[]).sort'

Works for me. What version are you using? Might be the old one wasn't actually marked nogc yet.

On Friday, 18 September 2015 at 02:24:44 UTC, Adam D. Ruppe wrote:
> Works for me. What version are you using? Might be the old one wasn't actually marked nogc yet.

I'm using the git head, must be a regression.

On Friday, 18 September 2015 at 02:29:55 UTC, Jack Stouffer wrote:
> On Friday, 18 September 2015 at 02:24:44 UTC, Adam D. Ruppe wrote:
>> Works for me. What version are you using? Might be the old one wasn't actually marked nogc yet.
>
> I'm using the git head, must be a regression.

Well apparently it's not, as I just used digger to check, and the digger version of dmd compiles it just fine. I'm not quite sure how a mis-build or something like that would manifest itself as a @nogc error though.

On Friday, 18 September 2015 at 02:21:13 UTC, Jack Stouffer wrote:
> The docs explicitly say that SwapStrategy.unstable is non-allocating, but this code (which is for finding the statistical mode of a range) will fail to compile.

Perhaps related to this issue you filed?

https://issues.dlang.org/show_bug.cgi?id=15003

sort calls assumeSorted, so it's affected by the same problem.