Re: [netmod] evaluating 'when' statements with unconfigured leafs

On Wed, Sep 25, 2019 at 8:37 AM Sterne, Jason (Nokia - CA/Ottawa) <
jason.sterne@nokia.com> wrote:

> Hi all,
>
>
>
> I saw some recent questions about 'when' statements. I had another one
> related to evaluating 'when' statements that involve leafs that don't
> currently have a value at all.
>
>
>
> leaf foo {
>
>     type enumeration {
>
>         enum val1;
>
>         enum val2;
>
>     }
>
> }
>
>
>
> leaf bar {
>
>     when "../foo != 'val2'";
>
>     type uint8;
>
> }
>
>
>
> Notice that foo does not have a default statement. So if no manager has
> set leaf foo, it doesn't exist in the config.
>
>
>
> In that case, does the "when" statement evaluate to 'true'  (i.e. leaf bar
> is allowed to have a value) ?
>
>
>

no

> i.e. assuming leaf foo is not set at all, is this accepted?
>
> <bar>23</bar>
>
>
>
> Or is there something special here because of the non-existence of leaf
> foo?
>
>
>

 correct.
An empty node-set does not always convert to am empty string.
So easy to tell XPath to do the wrong thing...

    when "../foo != 'val2'";

is not equivalent to

  when "string(../foo) != 'val2'";

If one object to be compared is a node-set and the other is a string, then
the comparison will be true if and only if there is a node in the node-set
such that the result of performing the comparison on the string-value
<https://www.w3.org/TR/1999/REC-xpath-19991116/#dt-string-value> of the
node and the other string is true.

Andy

If the "when" evaluates to 'false', then does the following "when" evaluate
> differently than the one above?
>
>     when "not(../foo = 'val2')";
>
>
>
> Jason
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