When lowering a foreach, the compiler gives priority to opSlice over front/popFront/empty, which is counter-intuitive (and also undocumented).

The following code, taken from [1] shows the issue: the overridden front in RangeWrapper is ignored when the wrapped range also defines opSlice, which is true for RangeT (the range returned by Array.opSlice). This causes the foreach output to be different from the expected old-style for loop equivalent.

Example code:
=====================================================
import std.stdio, std.container.array;
struct RangeWrapper(Range)
{
    Range range;
    alias range this;

    auto front()
    {
        return range.front + 1;
    }
}
auto rangeWrapper(Range)(auto ref Range range)
{
    return RangeWrapper!Range(range);
}
void main()
{
    Array!int array;
    array.insertBack(3);
	
    foreach (i; rangeWrapper(array[]))
        writeln(i);           // prints 3, which is wrong
	
    // isn't the above foreach equivalent to the following loop ?

    for (auto r = rangeWrapper(array[]); !r.empty; r.popFront())
        writeln(r.front);     // correctly prints 4
}
=====================================================

[1] http://forum.dlang.org/thread/fzwofczyvkxgmtvncmxb@forum.dlang.org