On 30/11/15 8:48 PM, Andrew LaChance wrote:
Hello,
D has intrigued me for a while, and I thought I would finally read up on
it! I've been reading "Programming in D" by Ali Çehreli and I've been
thinking about how I can use the language in a side project I'm working
on, porting it from java to D. One of the uncommonly-used features of
java that I like is how enums can be full classes (though I don't like
that there's no option to use enums as e.g. regular ints). This allows
several benefits, such as the ability to use them in switch statements
like regular enums, the full set of objects is known at compile time,
all objects are immutable, it's impossible to accidentally or
purposefully create new objects of that type, etc...
For example (in java), if I wanted to have an enum that describes all
the white keys on a piano keyboard and have members that describe the
number of half-steps to the next white key and to the previous white
key, I can define an enum (the "id" or enum value is implicitly defined
so it doesn't have to be explicitly written in the definition):
enum WhiteKey
{
A(2,2),
B(2,1),
C(1,2),
D(2,2),
E(2,1),
F(1,2),
G(2,2);
private final int halfStepsToNext;
private final int halfStepsToPrevious;
WhiteKey(int halfStepsPrevious, int halfStepsNext)
{
this.halfStepsToPrevious = halfStepsPrevious;
this.halfStepsToNext = halfStepsNext;
}
}
From what I've read and seen, in D all enums have forced to integral
types. Is it possible to do the above in D and I have just missed it?
I can think of a few ways around it (such as statically create and
define a bunch of WhiteKey structs, ...), but none are as clean as the
above. If this isn't something supported, is it on a roadmap of wanted
features?
Thanks! I'm looking forward to really getting to know the language.
enums don't have to be integral, but for performance reasons it is for
the best.
enum Foo : string {
A = "a",
B = "b",
C = "d",
ERROR = "What are you talking about?"
}
void main() {
import std.stdio : writeln;
Foo foo = Foo.ERROR;
writeln(foo, " is: ", cast(string)foo);
}
Also you are welcome in #d on Freenode (IRC) if you are interesting in
talking with the rest of us!
Btw you probably want tuples (std.typecons : tuple) to emulate those values.
