Implicit enum conversions are a stupid PITA

[bearophile]

To invent a software you can first find the best syntax. This seems a nice syntax, very similar to the enum one (that ubyte is optional):

flags ubyte Todo {
    do_nothing,
    walk_dog,
    cook_breakfast,
    deliver_newspaper,
    visit_miss_kerbopple,
    wash_covers
}

Todo todo = Todo.walk_dog | Todo.deliver_newspaper | Todo.wash_covers;
if (todo == (Todo.walk_dog | Todo.deliver_newspaper)) { ...
if ((Todo.walk_dog | Todo.deliver_newspaper) in todo) { ...
if ((Todo.walk_dog | Todo.deliver_newspaper) & todo) { ...
assert((Todo.walk_dog | Todo.walk_dog) == Todo.walk_dog); // OK


A way to implement it with current D2 syntax:


alias Flags!(ubyte, "do_nothing",
                    "walk_dog"
                    "cook_breakfast"
                    "deliver_newspaper"
                    "visit_miss_kerbopple"
                    "wash_covers") Todo;


Where Flags defines a struct, "do_nothing" are compile-time constants. It can overload 8 operators:
=   ==   |    |=    in   &   &=  opBool

The operator ! too can be defined, but I think it looks too much like the | so it can be omitted (other operators like ^ and ~ are possible).


Something like this can't work if enums become tidier:

enum ubyte Todo {
    mixin(Flags);
    do_nothing,
    walk_dog,
    cook_breakfast,
    deliver_newspaper,
    visit_miss_kerbopple,
    wash_covers
}



I don't like this:

mixin(Flags("
enum ubyte Todo {
    do_nothing,
    walk_dog,
    cook_breakfast,
    deliver_newspaper,
    visit_miss_kerbopple,
    wash_covers
}
"));




Something like can worl, but it's not nice:

struct Todo {
    mixin(Fields!(ubyte, "do_nothing",
                         "walk_dog"
                         "cook_breakfast"
                         "deliver_newspaper"
                         "visit_miss_kerbopple"
                         "wash_covers");
}



Once the programmer can define attributes, it can be doable this syntax that adds the required methods to the enum, but I am not sure:

@fields enum ubyte Todo {
    do_nothing,
    walk_dog,
    cook_breakfast,
    deliver_newspaper,
    visit_miss_kerbopple,
    wash_covers
}

Bye,
bearophile