How to pass a member function/delegate into a mixin template?

[John Colvin via Digitalmars-d-learn]

On Monday, 15 September 2014 at 13:50:22 UTC, 岩倉 澪 wrote:
> Hi all,
>
> I've been reading D Cookbook, in which the author recommends 
> the use of mixin templates to essentially hold boilerplate code 
> for classes (page 28). Referencing TDPL reaffirms this 
> strategy. With this design choice in mind, I would like to be 
> able to use a mixin template that creates a slot for me (as in 
> signals & slots) and provides a constructor that connects it to 
> the signal.
>
> The closest I have come is in the simplified example given 
> below:
>
> EventHandler event_handler;
>
> class EventHandler{
>     ...
>
>     mixin std.signals.Signal!Event;
>
>     ...
> }
>
> mixin template EventListener(void delegate(Event) slot){
>     private this()
>     in{ assert(event_handler); }
>     body{ event_handler.connect(&eventListener); }
>     private void eventListener(Event e){ slot(e); }
> }
>
> class Foo{
>     mixin EventListener!((e){ ... });
> }
>
> Sadly, this code does not compile.
> My understanding (and correct me if I'm wrong) is that this 
> does not compile because I cannot create such a delegate, as 
> the scope that it would be in is not available at compile time 
> (it would be objects instantiated from class Foo in this 
> example).
>
> One strategy that works is to not pass anything to the mixin 
> template, and have the mixin template use a function that is 
> presumed to exist. It is then the duty of the class writer to 
> make sure a function of the correct name and signature exists 
> if they use this mixin. However, I worry that this is 
> poor/brittle design.
>
> What is the best approach to achieve this?
>
> Thanks, Mio

would this work for you? "alias" is the usual way of taking a 
function as a template parameter.

mixin template EventListener(alias slot)