[Zope3-dev] zope.schema: defaults for non-immutables... questions

[Shaun Cutts]

Shane,

I considered 'default_factory' myself.... It seems good, but it
complicates the logic internally. For one thing, logically, we'd have to
also have 'missing_value_default' (unless we decree that missing values
have to be not-non-immutable, ah... immutable).

A further thought on where to put "filling in of defaults code" -- this
should probably be a separate routine in zope.schema:
setDefaults(instance)", which would set defaults (and validate? -- or
maybe call it "setDefaultsAndValidate").

- Shaun

PS anyone have idea or best practice on how to best through attributes,
avoiding shadowed ones? Seems like this is generally useful for
introspection of metadata.

-----Original Message-----
From: Shane Hathaway [mailto:shane at hathawaymix.org] 
Sent: Tuesday, January 24, 2006 12:39 PM
To: Shaun Cutts
Cc: zope3-dev at zope.org
Subject: Re: [Zope3-dev] zope.schema: defaults for non-immutables...
questions

Shaun Cutts wrote:
> It would seem that the current default mechanism is poorly suited to 
> providing default values for non-immutables. For example:

"Mutable" is a better way to say "non-immutable". :-)

> class IBar( Interface ):
> 
>     a = Object( schema = IFoo, default = Foo() )
> 
> But if a "Foo" is not immutable this doesn't make sense. (In my case,
I 
> want "a" to be a collection providing IFoo, which defaults to an empty

> collection. Each Bar implementing IBar should have its own instance of
Foo.)

I've run into this myself.  How about:

a = Object(schema=IFoo, default_factory=Foo)

?

Shane