[stringtemplate-interest] null vs missing vs empty vs nonexistent

[Zenaan Harkness]

On Fri, Oct 16, 2009 at 09:31:45PM -0700, Jonathan Buhacoff wrote:
> Hi, I've been lurking but would like to add my perspective here:
> 
> Where I grew up, null means missing value.

Hm. Must be a regional thing.

:) Couldn't resist sorry..


> I think it would be a  
> mistake to make a distinction between a key that was set with a  
> missing value, and a key that wasn't set at all. Either way the value  
> is missing.

What about a key (String) with value "" ?

This is strictly EMPTY as opposed to either NULL _or_ MISSING entirely.

Question is, how much to provide as _possible_ within pure ST, and how
much to push onto view-model.

> I think having an operator like ifnull is a great feature to have for  
> template authors that care for the difference between false and missing.

I have needed (and used the crude support for) if 'empty'.

Can you imagine real world cases where it's needed to handle the
differences between:

   -  TRUE vs FALSE

   -  "TRUE" vs "FALSE"

   -  attribute present  vs  no attribute present

   -  attribute NULL   vs  attribute has a value

   -  attribute = ""   vs   attribute !null, and "some string"

   -  attribute = "" or "   " or "\t", vs attribute contains
      "non whitespace"


> I also think that the if operator should treat null as false, for all  
> the template authors who care only if the value is defined and true.

How would this be implemented? A per-ST option?
Or perhaps:

   <names:{n | ...}; null=FALSE, empty=NULL>
   <names:{n | ...}; null=EMPTY, empty=NULL>  :)
   <names:{n | ...}; null=FALSE, empty=FALSE>

??


> I think that ifempty, trim, and other such variations should be left  
> to the model,  perhaps by wrapping strings with an object that  
> implements toString and also trim(), isEmpty(), etc.  so that the  
> template writer can make distinctions like $ifnull(value)$,   
> $if(value.isEmpty)$ and $if(value.trim.isEmpty)$

Good points. The ongoing question of course, is how much is good to put
into ST, and how much to require view-model munging.

If in ST, how do you feel about:

   <names:{...}; trim=TRUE; empty=FALSE>

?


cheers
zen

-- 
Homepage: www.SoulSound.net -- Free Australia: www.UPMART.org
Please respect the confidentiality of this email as sensibly warranted.