Enumap -- a lightweight AA alternative when your keys are enums

[SimonN via Digitalmars-d-announce]

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