On Wed, Aug 8, 2018 at 6:50 AM, Martin Bjorklund <[email protected]> wrote:
> Hi, > > "Sterne, Jason (Nokia - CA/Ottawa)" <[email protected]> wrote: > > Thanks William. > > Please see below. > > Regards, > > Jason > > > > > -----Original Message----- > > > From: Ivory, William <[email protected]> > > > Sent: Wednesday, August 8, 2018 3:27 AM > > > To: Sterne, Jason (Nokia - CA/Ottawa) <[email protected]>; > > > [email protected] > > > Subject: Re: [netmod] false() vs 'false' in 'when' statements > > > > > > On 07/08/18 18:37, Sterne, Jason (Nokia - CA/Ottawa) wrote: > > > Hi all, > > > > > > When comparing the value of a boolean leaf in a 'when' statement (or a > > > 'must' > > > statement), is an equality comparison to 'true' or 'false' the same as > > > a check > > > against true() or false() ? > > > > > > For example: > > > > > > leaf a { > > > type boolean; > > > } > > > leaf b { > > > type uint32; > > > when ".../a = 'true'"; > > > } > > > leaf c { > > > type uint32; > > > when ".../a = 'false'"; > > > } > > > (note that neither b nor c can be configured if leaf a isn't > > > explicitly configured > > > with a value since there is no default) > > > > > > If I replace the two 'when' statements above with the following > > > instead, is the > > > behavior the same ? > > > ... > > > when ".../a = true()"; > > > ... > > > when ".../a = false()"; > > > ... > > > > > > Or does "../a = true()" behave as an existence check on leaf a and > > > would be > > > enabled whether a is configured as true or false ? > > > > > > Regards, > > > Jason > > > > > > > > > > > > See https://www.w3.org/TR/1999/REC-xpath-19991116/#booleans > > > > > > (a) "../a = 'true'" > > > > > > Compares 'string-value' (same as value of node if a leaf, rather more > > > interesting if a list / container!) of each node in nodeset generated > > > by '../a' and > > > if any node in the nodeset matches 'true', expression is true. > > > > [>>JTS: ] In my specific example, leaf a is a single Boolean leaf. In > > that case, are these equivalent ? > > when ".../a = 'true'"; > > when ".../a = true()"; > > No... > > > and are these also equivalent ? > > when ".../a = 'false'"; > > when ".../a = false()"; > > .... and no. > > What you probably want is ".../a = 'true'" (or 'false'). > > The expression: > > ".../a = true()"; > > will first take the string value of ".../a", which e.g. is "false". > This string value is then converted to a boolean, resulting in the > boolean value True (b/c the string is non-empty). > > This means that if "a" is set at all (to true or false), the > expression ".../a = true()" returns true. The expression ".../a = > false()" will only return true if "a" is unset. > > I suggest reading the XPath definition of boolean comparisons: https://www.w3.org/TR/1999/REC-xpath-19991116/#booleans It is a bit complicated, but generally, a node-set is converted to a boolean (==false for empty, ==true for not empty) when compared to a boolean for equality/inequality. false is a boolean 'false' is a string false() is a function that return a boolean Andy > (sorry if I'm being dense here, but I'm not 100% positive if I'm > > interpreting your explanations correctly and getting the right > > conclusion. I've never seen must or when statements that use = > > false() or = true()). > > > > [>>JTS: ] Are the strings 'true' and 'false' the "string-value" (that > > you mention above) for a Boolean leaf ? > > Yes, according to 9.5.1 in RFC 7950. > > > 'a' is a single Boolean leaf so the nodeset is that single leaf and > > the value is 'true' or 'false'. > > > > > > > > (b) "../a = true()" > > > > > > Similar to above but after getting the string-value, this is converted > > > to a > > > boolean before comparing with the boolean true. > > > > [>>JTS: ] I'm a bit confused here. Are you saying that the > > string-value of leaf a is converted to a Boolean ? > > Do the string-values of a convert to something that is equal to true() > > or false() ? > > See above. > > > /martin > > > > > > > > > > (c) '../a' > > > > > > True if the nodeset generated by this expression is not empty. > > > > > > --- > > > > > > Caveats alluded to above are that if '../a' matches multiple nodes, > > > then only > > > one of these nodes needs to pass the test for the test to be true. > > > Separately, if > > > any of the nodes are not leaves, the 'string-value' is a concatenated > > > string of > > > the values of the node's child / grandchild leaves. > > > > > > Hope that helps. You wouldn't believe the number of unit tests I have > > > to make > > > sure we get this logic right! Using '!=' when comparing a nodeset > > > with >1 node > > > with other values is very likely not to give the answer you expect (-: > > > > > > Regards, > > > > > > William > > > > > > > _______________________________________________ > > netmod mailing list > > [email protected] > > https://www.ietf.org/mailman/listinfo/netmod > > > > _______________________________________________ > netmod mailing list > [email protected] > https://www.ietf.org/mailman/listinfo/netmod >
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