problem with custom predicate

[Steven Schveighoffer via Digitalmars-d-learn]

On 5/27/15 9:11 AM, "Simon =?UTF-8?B?QsO8cmdlciI=?= 
<simon.buerger at rwth-aachen.de>" wrote:
> On Wednesday, 27 May 2015 at 14:58:39 UTC, drug wrote:
>
>> Do you want to dynamically change priority?
> Actually yes. In my actual code I am not using a RedBlackTree but my own
> Container (a heap with the possibility to modify elements inside), which
> is notified when prio changes so it can do a (local) reordering.

It would be a very bad idea to change prio if the RBTree is constructed 
already (and if this works).

>> Why prio is outside of your predicate?
> Well, how would I get it into the lambda? In C++ I would use a
> comparision class, and the constructor of the container would take an
> instance of that class. But D's RedBlackTree-constructor does not take
> such a (run-time) argument. And I dont see a way to get prio into the
> predicate, which is a template-argument.

This is true, RedBlackTree does not take a functor as a parameter to the 
constructor, it just uses an alias.

This should work if your RedBlackTree is scoped inside a function where 
the data exists. But at the time of declaration inside the class, the 
instance of prio doesn't exist, so you can't alias it.

It would be a good enhancement I think to add support for function objects.

-Steve