for discussion None vs null: vs current:

[Robert Collins]

On Thu, 2006-07-20 at 23:21 +1000, Martin Pool wrote:
> On 19 Jul 2006, Robert Collins <robertc at robertcollins.net> wrote:
> 
> > EMPTY_REVISION - 'empty:'
> 
> This needs to represent both value (contains nothing) and identity
> (ultimate ancestor).  "empty" might suggest it just happens to be empty?
> The word "root" is used for too many other things but how about
> "origin:"?  I could live with "empty:" though.

origin does not imply empty either :). I think its better to imply the
state of the tree, rather than what we use it for.

> > NULL_REVISION - 'null:'
> 
> And what will this actually do?

its a revision, but an unknown one. Contrast with NOT_A_REVISION, which
is not a revision.

> > CURRENT_TREE_REVISION - 'current:'
> 
> OK
> 
> > None aka NOT_A_REVISION - ':'
> 
> Let's make it "not_a_revision:" or something then, unless there's any
> compelling reason it needs a one-character name?

Well, I want to use it to delimit revision lists in a line based file
format, so not_a_revision: is very verbose compared to just ':'.

> > open discussion points:
> >  * should we use other delimiters than :.
> >  * does NOT_A_REVISION make sense?
> 
> Only if you can think of a plausible case where it will occur?  Maybe
> having decided on it we should add it as a comment to revision.py but
> not use it yet.
> 
> I think reserving revision ids ending with : for this is fine, and in
> general treating the bit before the first colon as a namespace that
> needs to be coordinated is also fine.

Cool. I have a use for NOT_A_REVISION right now in a plugin I'm fiddling
with.

Rob


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