[Chandler-dev] a new kind of enumeration type

[Phillip J. Eby]

We could do that, after we got rid of any existing code that depends on the 
old semantics of enumerations.

However, it should be noted that this may lead to interesting problems in 
schema upgrades.  My understanding is that the reason for wanting explicit 
values (as opposed to simple sequence) is that it allows constant values to 
be preserved across releases, even if things are added or removed.  Second, 
it allows the use of enumerations as constants for interacting with 
external systems, like socket mode flags and such.

At 03:04 PM 8/30/2006 -0700, Grant Baillie wrote:
>Perhaps I should've been more explicit :o). Instead of
>
>     class TriageEnum(schema.Enumeration):
>         values = {"now": 0, "later": 1, "done": -1}
>
>I would rather just write:
>
>     class TriageEnum(schema.Enumeration):
>         values = "done", "now", "later"
>
>to produce the same values TriageEnum.done, TriageEnum.now, etc. (The
>values would be auto-generated, but would sort the same as the dict
>example).
>
>--Grant
>
>
>On 30 Aug, 2006, at 14:38, Phillip J. Eby wrote:
>
>>Because dictionaries aren't ordered.
>>
>>At 02:07 PM 8/30/2006 -0700, Grant Baillie wrote:
>>>Hmm.... Why not just have the declaration order be the sort order?
>>>
>>>--Grant
>>>
>>>On 30 Aug, 2006, at 13:57, Andi Vajda wrote:
>>>
>>>>
>>>>While implementating Chandler's dashboard Bryan found that he
>>>>needed better control over the sorting of enumeration values.
>>>>
>>>>Currently, enumeration values are strings and are sorted as such.
>>>>For example, if one defines an enumeration with the schema API as
>>>>follows:
>>>>
>>>>    class TriageEnum(schema.Enumeration):
>>>>        values = "now", "later", "done"
>>>>
>>>>The values of this enumeration will be sorted as:
>>>>     "done" < "later" < "now"
>>>>
>>>>
>>>>Enter a new type of enumeration, an enumeration of constants. Such
>>>>constants have a name and a value and are sorted on their value
>>>>first. Multiple constants in an enum may have the same value, their
>>>>name is used next in sorting.
>>>>
>>>>By using a dict for the enumeration's values instead of a tuple,
>>>>one can define such a constant enumeration with the schema API:
>>>>
>>>>     class TriageEnum(schema.Enumeration):
>>>>         values = {"now": 0, "later": 1, "done": -1}
>>>>
>>>>Upon definition, the TriageEnum class gets assigned three
>>>>attributes called 'now', 'later' and 'done' that contain such a
>>>>constant:
>>>>
>>>>    TriageEnum.now -> TriageEnum.now
>>>>    TriageEnum.now.value -> 0
>>>>    TriageEnum.now.name -> 'now'
>>>>
>>>>    repr(TriageEnum.now) -> 'TriageEnum.now'
>>>>    str(TriageEnum.name) -> 'now'
>>>>
>>>>These constants are sorted by their values:
>>>>     TriageEnum.done < TriageEnum.now < TriageEnum.later
>>>>
>>>>Andi..
>>
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