What is the appropriate way to create a variable for the range
returned by RedBlackTree lowerBound and upperBound. For example,
given this code:
```
RedBlackTree!long promptPosition = redBlackTree!long();
long row = to!long(vte.getVadjustment().getValue());
RBRange!(RBNode!long*) range;
if (direction < 0) {
range = promptPosition.lowerBound(row);
if (range.empty) result = lower;
else result = range.back;
} else {
range = promptPosition.upperBound(row);
if (range.empty) result = upper;
else result = range.front();
}
if (result >= lower) {
vte.getVadjustment.setValue(to!double(result));
} else {
promptPosition.remove(range);
}
```
The second line where I declare the range variable as
RBRange!(RBNode!long*) the compiler complains with the following
warning:
Deprecation: std.container.rbtree.RBRange(N) is not visible from
module terminal
Which makes sense since RBRange is a private struct. However I
cannot use the normal range interfaces here either (ForwardRange,
BiDirectionalRange, etc) since it complains about RBRange not
being able to cast to them.
