On Aug 29, 2005, at 4:50 PM, Jim Fulton wrote:
Gary Poster wrote:
...
4 Recognize and document that the 'default' field argument is
actually 'initial value'. That is, if you set a field with a
default to the missing_value, the default does not become the
field's value: the 'default' value is only used if the value has
never been set (i.e., during creation or when there is no
previous state of the value). Possibly rename to
'initial_value' (with deprecation support). *would need proposal*
5 Allow fields to accept a default (or initial_value, as above)
*or* a default_getter (or initial_value_getter, as above).
default_getter/ initial_value_getter would be a callable passed
the field's context. It should return the desired initial
value. Use cases include initializing to now, today, the current
user, etc. *would need small proposal* *code exists*
I'm uncomfortable with this. Right now, I think fields do too much.
They have too much application logic. This would add more. The whole
concept of "initial value" seems to be very application dependent.
Maybe it would be best to just drop the default field altogether
and introduce adapters for computing initial values in those special
cases when we need them.
Initial value is a concept in XMLSchema (http://www.w3.org/TR/
xmlschema-1/#key-iv). The qoute is in W3C-speak, but I'm pretty sure
they are talking about what we are talking about. I think it does
belong in a statement about a logical schema.
Moreover, I regard any lookup code as an intellectual cost for
developers: a cost both for making and for finding the associated
configuration. For schemas, being able to look in one place is very
valuable, at least to me. APIDoc can help, but is not a panacea. I
don't think this particular configuration division would be a win.
I think dropping the functionality of default would be a loss for
reasonable schema functionality. I think renaming it to initial or
initial_value would be a win for accurate names. I'm willing to drop
the getter: it is kind of ugly, I admit.
You ok with just changing the name?
...
7 add combination field and widget to schema and form,
respectively. A combination field allows a user to fill in
multiple values simultaneously, and returns a tuple of the
combined values. Use cases overlap somewhat with object field/
widget, but this is simpler to use for simple use cases. Use
cases include range fields. *would need small proposal* *code
exists*
I have an open mind, but I'm a bit skeptical (as you know :). I
expect
this proposal to be a bit controversal. Perhaps we can plan to go
another
round of brainstorming during the sprint.
OK--I must admit that I have a bit of the "hack" willies about it
too. :-) It's useful, though, and I haven't been convinced by any
alternatives yet. This one's off the table for the sprint then,
except perhaps for discussion.
For the record, here are the use cases that the Combination field
fills now:
- range
- main value plus modifier(s): find something supervised by X (a
person), directly or indirectly (a Bool); and select something for
publication (an object), in a given context (local, global, whatever).
I know you don't like the first one, and I do ATM :-). The second
one makes me more suspicious, though. A combination field can
fulfill it, but we have had a real use case, or at least desire, for
a list widget of this sort of data structure. Without a concept of
"main value" and "secondary values" (and a combination widget doesn't
promise anything like that) you can't get what we wanted.
10 The big restructuring of schema: divide up schema into
interface values and usage relationships. This is too big to
explain in this email, and probably too big to even adequately
begin in two days. This is the direction Jim wants to take
schema, though, and I'm +1.
See:
http://mail.zope.org/pipermail/interface-dev/2004-June/000048.html
Cool, thanks.
Gary
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