On Wed, Sep 7, 2016 at 7:02 PM, Dale R. Worley <wor...@ariadne.com> wrote:
> Andy Bierman <a...@yumaworks.com> writes: > > Using a key of type empty is utterly pointless unless the point > > is to make the instance identifier longer. > > IMO using a key of type empty (or any type with only one value) is > *pointless* but should be *valid*. Things should be valid unless > processing them according to the ordinary rules can't work. Indeed, > specifically banning them increases the complexity of the > specification. > > It is both pointless and valid. > The reason for this is that the code (in this case, the module > definition) may be generated by an automatic process, and those > processes are easier to construct if the rules contain fewer > irregularities. E.g., multiplying a number by zero is pointless, in > that the result is always zero, and one might ask, Why not just write 0 > instead of the multiplication? But everyone agrees that the statement > > a = 0 * b; > > is *valid*, and can easily imagine situations where a process might > generate it as an output. > > Not sure that this has to do with YANG list keys. > >> Unless I'm off, the line should be fixed to avoid the string > >> conversion: > >> > >> /ex:system/ex:service[ex:name='foo'][ex:enabled] > >> > >> and a negation should be: > >> > >> /ex:system/ex:service[ex:name='foo'][not(ex:enabled)] > > > > There is only one value provided by type empty. The 2nd instance > > identifier is invalid. > > There is no instance possible that does not include the 'enabled' leaf. > > The 2nd instance identifier is (should be) *valid* even if it always > returns the empty set. (Assuming it is used in contexts where a set can > be returned.) > I disagree -- an instance identifier has a strict syntax. The 2nd expression is valid XPath (again, pointless and valid) > > Dale > Andy
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