Code:
-------
unittest
{
    import std.algorithm.comparison : equal;
    import std.algorithm.iteration : chunkBy;

    string[] data = [ "abc", "abc", "def" ];
    int[] indices = [ 0, 1, 2 ];

    auto chunks = indices.chunkBy!((i, j) => data[i] == data[j]);
    assert(chunks.equal!equal([ [ 0, 1 ], [ 2 ] ]));
}
-------

Compiler output:
-------
/usr/src/d/phobos/std/algorithm/iteration.d(1761): Error: function test.__unittest_L9_C1.ChunkByImpl!(__lambda1, int[]).ChunkByImpl.Group.popFront cannot access frame of function test.__unittest_L9_C1
/usr/src/d/phobos/std/range/primitives.d(884): Error: template instance `std.range.primitives.isInputRange!(Group)` error instantiating
/usr/src/d/phobos/std/algorithm/iteration.d(1781):        instantiated from here: isForwardRange!(Group)
-------