Re: [Templates] TT in callback

> Rather than copying the entire variable stash each time we need to

Andy Wardley wrote:
> Rather than copying the entire variable stash each time we need to 
> create a localised variable scope (e.g. INCLUDE), TT3 creates a new, 
> empty variable stash with a parent link pointing upwards to the stash 
> of the calling context.  
> 
> When a variable is first accessed, the stash fetches it from a parent, 
> grandparent, great-grandparent, etc., walking up through the ancestral 
> family tree until the variable is located.  It then copies it into the 
> current local stash, effectively caching it for any subsequents access.  
> Any new variable values are written into the local stash, leaving any 
> previous values untouched in the parent, grandparent, etc.  At the end 
> of the template, the local stash is throw away and we revert to the 
> parent stash.

I like this a lot.  That way, when a template developer does the right 
thing, he also makes it more efficient at the same time.  i.e., the 
right thing to do, as I see it, is to treat an included template like a 
sub, and only use inside it the variables that are passed as parameters. 
  That way you avoid both the overhead of copying and the dangers of 
side effects.

BTW, I just read in the documentation for INCLUDE that the localization 
is only skin-deep.  So in TT2 INCLUDE would only have a large 
performance penalty vs. PROCESS if you have a lot of top-level template 
variables.  In TT3, with on-demand copying, will they still only be 
skin-deep?

TTYL,
Chad.

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