I frequently find myself needing a data structure that maps each member of an enum to a value;
something similar what Java calls an EnumMap (http://docs.oracle.com/javase/7/docs/api/java/util/EnumMap.html).

I couldn't find any D implementation out there, so I wrote a little module for it.
Enumap is available on Github (https://github.com/rcorre/enumap)
and via dub (http://code.dlang.org/packages/enumap).
Docs are hosted at http://rcorre.github.io/enumap/.

An Enumap is basically a thin wrapper that makes a static array look like an associative array:

---
enum Attribute {
 strength, dexterity, constitution, wisdom, intellect, charisma
}

Enumap!(Attribute,int) attributes;
attributes[Attribute.strength] = 10;
---

However, you might prefer an Enumap to an associative array if:

You like syntactic sugar:
---
// Boring!
if (hero.attributes[Attribute.wisdom] < 5) hero.drink(unidentifiedPotion);

// Fun! And Concise!
if (hero.attributes.wisdom < 5) hero.drink(unidentifiedPotion);
---

You like ranges:
---
// roll for stats!
attributes = generate!(() => uniform!"[]"(1, 20)).take(6);
---

You like default values:
---
int[Attribute] aa;
Enumap!(Attribute, int) em;

aa[Attribute.strength]; // Range violation!
em.strength;            // 0
---

You like array-wise operations:
---
// note the convenient constructor function:
auto bonus = enumap(Attribute.charisma, 2, Attribute.wisdom, 1);

// level up! adds 2 to charisma and 1 to wisdom.
hero.attributes += bonus;
---

You dislike garbage day:
---
      void donFancyHat(int[Attribute] aa) { aa[Attribute.charisma] += 1; }
@nogc void donFancyHat(Enumap!(Attribute, int) map) { map.charisma += 1; }
---

Check it out, report bugs and all that!

P.S.

The above example used to read:
attributes = sequence!((a,n) => uniform!"[]"(1, 20)).take(6);
before Gary's recently posted article at http://nomad.so/2015/08/more-hidden-treasure-in-the-d-standard-library/ made me realize generate existed.

On Friday, 11 September 2015 at 02:17:25 UTC, rcorre wrote:
> I frequently find myself needing a data structure that maps each member of an enum to a value;
> something similar what Java calls an EnumMap (http://docs.oracle.com/javase/7/docs/api/java/util/EnumMap.html).
>
> I couldn't find any D implementation out there, so I wrote a little module for it.
> Enumap is available on Github (https://github.com/rcorre/enumap)
> and via dub (http://code.dlang.org/packages/enumap).
> Docs are hosted at http://rcorre.github.io/enumap/.

Hi,

this looks excellent! I've been playing around with it, and am looking forward to using it regularly.

I've ran into a compilation error when iterating over a const Enumap. In the following code:

    import std.stdio;
    import std.conv;
    import enumap;

    enum MyEnum { e1, e2, e3 }

    struct A
    {
        Enumap!(MyEnum, int) map;

        void mutable_output()
        {
            foreach (MyEnum e, int i; map)
                writefln("%s: %d", e.to!string, i);
        }

        void const_output() const
        {
            foreach (MyEnum e, const int i; map)
                writefln("%s: %d", e.to!string, i);
        }
    }

...the first method (mutable_output) compiles and works with no errors. The const method, however, gives:

    source/app.d(19,13): Error: invalid foreach aggregate this.map,
    define opApply(), range primitives, or use .tupleof".

It doesn't seem to matter whether I put const int, or int, in the foreach statement.

What's the idiomatic way to loop over a const Enumap? :-)

-- Simon

On Friday, 11 September 2015 at 03:25:58 UTC, SimonN wrote:
> Hi,
>
> this looks excellent! I've been playing around with it, and am looking forward to using it regularly.
>
> I've ran into a compilation error when iterating over a const Enumap. In the following code:
>
>     import std.stdio;
>     import std.conv;
>     import enumap;
>
>     enum MyEnum { e1, e2, e3 }
>
>     struct A
>     {
>         Enumap!(MyEnum, int) map;
>
>         void mutable_output()
>         {
>             foreach (MyEnum e, int i; map)
>                 writefln("%s: %d", e.to!string, i);
>         }
>
>         void const_output() const
>         {
>             foreach (MyEnum e, const int i; map)
>                 writefln("%s: %d", e.to!string, i);
>         }
>     }
>
> ...the first method (mutable_output) compiles and works with no errors. The const method, however, gives:
>
>     source/app.d(19,13): Error: invalid foreach aggregate this.map,
>     define opApply(), range primitives, or use .tupleof".
>
> It doesn't seem to matter whether I put const int, or int, in the foreach statement.
>
> What's the idiomatic way to loop over a const Enumap? :-)
>
> -- Simon

Interesting, thanks for pointing that out.
I don't think I did a great job with const-correctness here, I'll take a look tomorrow.
It should definitely be possible to iterate over (and index, etc...) a const/immutable Enumset, though you're right that it doesn't work right now.

On Friday, 11 September 2015 at 04:02:17 UTC, rcorre wrote:
> On Friday, 11 September 2015 at 03:25:58 UTC, SimonN wrote:
>> Hi,
>> I've ran into a compilation error when iterating over a const Enumap. In the following code:
>
> Interesting, thanks for pointing that out.
> I don't think I did a great job with const-correctness here, I'll take a look tomorrow.
> It should definitely be possible to iterate over (and index, etc...) a const/immutable Enumset, though you're right that it doesn't work right now.

No worries, take your time! Thanks for the quick clarification.

I've also tested a couple ways of assigning in a foreach. Continuing from my code above (struct A { Enumap!(MyEnum, int) map; /* ... */ }), I've tried this in the main function:

    int some_value = 100;
    A a;

    foreach (MyEnum e, ref val; a.map)
        val = ++some_value;
    a.mutable_output();

    foreach (MyEnum e, ref val; a.map)
        a.map[e] = ++some_value;
    a.mutable_output();

Output:

    e1: 0
    e2: 0
    e3: 0
    e1: 104
    e2: 105
    e3: 106

Since I have been using "ref val" in the first loop, I expected the output to be instead:

    e1: 101
    e2: 102
    e3: 103
    e1: 104
    e2: 105
    e3: 106

-- Simon

On Friday, 11 September 2015 at 02:17:25 UTC, rcorre wrote:
> @nogc void donFancyHat(Enumap!(Attribute, int) map) { map.charisma += 1; }

BTW, what this means? Isn't Enumap a value type?

On Friday, 11 September 2015 at 04:30:31 UTC, SimonN wrote:
>
> Since I have been using "ref val" in the first loop, I expected the output to be instead:
>
>     e1: 101
>     e2: 102
>     e3: 103
>     e1: 104
>     e2: 105
>     e3: 106
>
> -- Simon

Yep, as I was looking at the constness thing, I realized that ref parameters in foreach are totally broken. I may just have to use opApply instead of opSlice.

On Friday, 11 September 2015 at 08:22:20 UTC, Kagamin wrote:
> On Friday, 11 September 2015 at 02:17:25 UTC, rcorre wrote:
>> @nogc void donFancyHat(Enumap!(Attribute, int) map) { map.charisma += 1; }
>
> BTW, what this means? Isn't Enumap a value type?

Correct, the parameter should be passed by ref in that example. Good catch!

On Friday, 11 September 2015 at 03:25:58 UTC, SimonN wrote:
>
> It doesn't seem to matter whether I put const int, or int, in the foreach statement.
>
> What's the idiomatic way to loop over a const Enumap? :-)
>
> -- Simon

I've released v0.4.0, which implements foreach with ref, and (hopefully) atones for my crimes against const-correctness. You should be able to modify values in a loop and work with const/immutable Enumaps.

Thanks for the feedback!

On Sunday, 13 September 2015 at 03:33:15 UTC, rcorre wrote:
> I've released v0.4.0, which implements foreach with ref, and (hopefully) atones for my crimes against const-correctness. You should be able to modify values in a loop and work with const/immutable Enumaps.
>
> Thanks for the feedback!

Yes, the 0.4.x version works with my examples perfectly. Thanks for adding const support!

(I haven't tested yet every combination of const/mutable Enumap, const/mutable foraech-value, and direct/ref foreach-value. My examples are exactly what I'd do in normal projects anyway, mapping enum-values to ints.)

-- Simon

On Wednesday, 16 September 2015 at 03:20:28 UTC, SimonN wrote:
> Yes, the 0.4.x version works with my examples perfectly. Thanks for adding const support!
>
> (I haven't tested yet every combination of const/mutable Enumap, const/mutable foraech-value, and direct/ref foreach-value. My examples are exactly what I'd do in normal projects anyway, mapping enum-values to ints.)
>
> -- Simon

Good to hear!
I have a pretty long set of static asserts that tries every (?) operation between mutable/const/immutable enumaps to verify that they do/don't compile as expected, so hopefully that has most situations covered.