On 2019-12-12 02:59, Alan Evans wrote:
I love Automatic Parameter Lookup (APL) and hiera in general. But one
thing I have found awkward is that `lookup_options` are found in the
hiera data. In general the idea is to separate data from code right?
Exactly, and that is why the options should be in the data because that
is the place where data structure was defined!
As an example you may not want to have merging at all and override
a value with a complete hash. You don't want to change a manifest to do
that.
Lookup options do not feel like data to me, but more like something I
would find in the code the same way in the code I can type class parameters.
> *Proposal*
Create a data type (or function perhaps that returns a data type) that
tells the APL code HOW to do the lookup. The lookup key is just the
class/name of the current param and the rest of the arguments could
behave like lookup().
|
classfroboz(
Array[String]$my_param =LookupOptions('unique'),
Hash $options
=LookupOptions('deep',knockout_prefix=>'-',default_value=>undef),
){# Do Useful Stuff}
|
Or maybe just *Lookup* with a capital *L* or perhaps a function
*lookup_options()* that returns some internal class/data type that need
not be visible to the puppet user.
|
classbozfro(
$some_param =Lookup(Array[String],'unique',undef),
$another_param =lookup_options(Hash,'deep',{knockout_prefix =>'-'}),
){# Do Useful Stuff}
|
A default value expression is evaluated if there were no data given in
the manifest and if no data was found when doing a lookup. So, cannot
use the default value expression to try to influence the lookup as that
would break the contract of when those are evaluated.
Do you think lookup_options seem out of place in the hiera data?
No they are at the right place.
Would it make more sense as a Data Type or a function() w/ some
invisible data type that APL uses?
You would then need to invent new syntax.
Does this belong in puppet proper? Stdlib? (Could it go in stdlib?)
It cannot go into stdlib it would need to be an integral part of the
language.
You either use APL and stick the options into hiera as needed, or you
do not bind to any APL looked up keys and use an explicit lookup in the
default value expression. If you do that then you can specify the
options in your manifest.
I recommend using APL.
- henrik
Please discuss.
-Alan
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