RBTree delegates and types

[Steven Schveighoffer]

On 3/19/18 5:16 AM, Viktor wrote:

> 
> Hi Steve, thanks for replying!
> 
> I've also noticed that RedBlackTree.opEquals() is like this from the 
> initial pull request and was wondering if noone has been using a 
> delegate and why...

typically, you don't need a delegate, but generally, you CAN use a 
delegate as an alias "less" function. I don't see why it should be 
restricted here.

But this is probably why nobody ever found it -- most people just use 
the default lambda.

> 
> On the second topic, I've tried that and it doesn't work. I have a 
> minimal test program that shows the issue.
> 
> https://run.dlang.io/is/WNF78H

Oh! I totally missed that comp is a member function (in your first 
example). I thought it was passed in. Sorry for not taking a closer look.

Yes, you need a `this` pointer for it to work. However, we can do this 
by encapsulating the return type with an auto function:

https://run.dlang.io/is/inSzaU

Sorry I didn't get this right away. Interesting chicken-and-egg problem, 
but as usual, D delivers :)

-Steve