Enums - probably an old subject

[inout]

On Thursday, 21 November 2013 at 17:19:18 UTC, inout wrote:
> On Thursday, 21 November 2013 at 07:22:39 UTC, Steve Teale 
> wrote:
>> import std.stdio;
>>
>> enum Intention
>> {
>>   EVIL,
>>   NEUTRAL,
>>   GOOD,
>>   SAINTLY
>> }
>>
>> void foo(Intention rth)
>> {
>>   if (rth == EVIL)
>>      writeln("Road to hell");
>> }
>>
>>
>> void main()
>> {
>>   foo(EVIL);
>> }
>>
>>
>> Why does the compiler complain in both places about EVIL. Can 
>> it not work out which EVIL I mean? There's only one choice.
>
> Because of the follwoing:
>
> import foo.bar;
>
> enum Intention
> {
>   EVIL,
>   NEUTRAL,
>   GOOD,
>   SAINTLY
> }
>
> void foo(Intention rth)
> {
> ...
> }
>
> void main()
> {
>   // imagine that this works
>   foo(EVIL);
> }
>
> module foo.bar;
>
> // someone else adds this later
> enum OtherIntention
> {
>   EVIL,
>   NEUTRAL,
>   GOOD,
>   SAINTLY
> }
>
> BOOM! Code no longer compiles.
>
> As a rule, the code that compiles and works should preserve its 
> behavior when new code is added, so this is prohibited.
>
> Also please post to D.learn

forgot to add:

void foo(OtherIntention rth) { ... }

Which of the two is being called by main?