On 25/02/16 23:50, Trevor Vaughan wrote:
I just want to make sure I'm reading this right.
For the first scenario, noop means don't order anything, just do things
in whatever order they happen.
And the second scenario is: don't fail B if A fails (don't create a
relationship), but do A before B
Is this correct?
I have problems understanding what you mean by noop and fail here.
The fundamental question is, does this expression define the order of A
and B?
A -> [ ] -> B
You can view it either as it defines the order [A, B], or that it does
not and their partial order is unaffected.
If you like the answer to be [A, B], does it bother you that the
following is not the same thing:
A -> [ ]
[ ] -> B
As that would not order them - because [ ] here can be seen as either
first/last or "in the partial order that is defined elsewhere".
Trying to make that define the order [A, B] is impossible since every
resource starts out with the partial order [[], R, []] (nothing before
R, nothing after R).
- henrik
If it is, I favor the second scenario as the default as it is more
intuitive to the 'ordered compile' of Puppet 3+.
Thanks,
Trevor
On Thu, Feb 25, 2016 at 5:31 PM, Henrik Lindberg
<henrik.lindb...@puppetlabs.com <mailto:henrik.lindb...@puppetlabs.com>>
wrote:
On 25/02/16 22:08, John Bollinger wrote:
On Thursday, February 25, 2016 at 8:55:01 AM UTC-6, Trevor
Vaughan wrote:
Hmm.....
I think, as long as it is documented, then whatever behavior is
deterministic is fine.
'
I think that there is value in the following resolutions:
Notify['left'] -> [] -> Notify['right']
* Noop since there is nothing in []
Notify['left'] -> [] -> Notify['right']
Notify['left'] -> Notify['right']
* First == Noop
* Second == Expected ordering
I flip-flopped a bit on this. I started from the position that
it would
be inappropriate for
|
Notify['left']->$stuff ->Notify['right']
|
or
|
Notify['left']->Stuff<||>->Notify['right']
|
ever to fail to cause Notify['left'] to be applied before
Notify['right'], as indeed it now does fail to do in the event
that the
stuff in the middle represents zero resources. My basis there
was that
it is counterintuitive for such expressions to not establish
relative
ordering of the two Notifys.
Ultimately, however, that basis is completely subjective.
Others might
reasonably intuit that such an expression would have exactly the
semantics it actually does have, which are roughly equivalent to
those of
|
Notify['left']->$stuff
$stuff ->Notify['right']
|
. Upon reflection, this alternative is less magic. It falls out
naturally from understanding that chain operators associate from
left to
right, and that each binary chain expression /evaluates to/ the
value of
its right-hand operand. That some people might find that behavior
surprising is a consideration, but not a primary one for me.
It depends on the operator if it is left or right associative and if
it is cumulative. And also what the result of '(nothing) op
(something)' results in.
if
(nothing) -> X
X -> (nothing)
both evaluate to X
as in
0 + 1
1 + 0
Then empty man in the middle would be a noop.
If you consider the arrows to abstractly order a set of resources in
an array which at the end of the chain defines the partial order of
the resources it would be the same as doing array concatenation.
i.e.
[A] + [] + [B] = [A, B]
So - it is all down to definition of the arrow operators; i.e.
taste/most practical/least surprise.
- henrik
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