Problem Instantiating a BinaryHeap with a Comparison Function the needs this

[Nordlöw]

I can understand how to correctly define an instance of 
BinaryHeap in my class DijkstraWalker at

https://github.com/nordlow/justd/blob/master/knet/traversal.d#L264
because the comparsion function can't ge access to the class 
member distMap

I get the error

need 'this' for 'distMap' of type 'Tuple!(double, 
Ref!(Node))[Ref!(Node)]'

What to do?