problem with custom predicate

[Steven Schveighoffer via Digitalmars-d-learn]

On 5/27/15 9:59 AM, Meta wrote:
>
> I thought unaryFun *does* work with all callables, including
> structs/classes with opCall?

It (binaryFun actually) declares an alias. But you need an actual 
instance to use in this case. You simply can't declare that in a type 
definition, and it won't be set up properly in the constructor even if 
you could. You need an instance in order to use an alias to that instance.

What likely would happen is if the functor is a callable type, and that 
type is not a functor itself (i.e. doesn't define static opCall), is 
that RedBlackTree would then require an instance of that type as part of 
the constructor.

-Steve