two questions on enums

[Chris Williams]

On Thursday, 3 April 2014 at 23:16:14 UTC, Eric wrote:
> Okay - I'm new to D, and I'm comming from a java background.  
> Suppose
> you are designing an API, and you want the user to supply 
> arguments
> as an enum.  But the user needs to define the enum, so how can 
> the API
> know in advance what enum to require?  The solution is to 
> require an
> enum that implements a known interface.  This is easy to do in 
> java,
> but I haven't yet tried it in D.  I suspect it could be done 
> with CTFE
> or something.  An example where I use this is for electronics 
> software.
> If I need the user to supply a set of pins, the pins are 
> supplied as an
> enum which implements an interface.  By using the interface, it 
> also
> forces the user to include all of the attributes of each pin 
> such as
> direction, max load, DC current, etc.  Since class type enums 
> are references,
> they are light, - and they should be immutable - so they are 
> thread safe aslo.

I'm not sure how you're using your enum. In Java, the only way to 
perform a switch over an enum is if you know all the values 
during compile time. Passing a type Enum into a function (i.e. as 
opposed to "enum MyEnumType') requires using introspection to 
pull the actual values out, and then a loop to scan through them 
for your target value.

But if you've programmed a switch for a known enum type, then 
that means the enum has already been implemented and there is no 
chance for more than one type to be passed in.

So I'm confused.