On 2014-06-08 19:29, Wil Cooley wrote:
On Aug 5, 2014 6:41 PM, "Reid Vandewiele" <[email protected]
<mailto:[email protected]>> wrote:
> Example 1 (assuming behavior whereinmerging is OK, and that explicit
parameter specification takes precedence):
>
> apache::vhost { $servername:
> port => $port,
> ssl => $ssl,
> attribute_defaults => $extra_opts,
> }
Assuming that the semantics of 'undef' haven't changed to preclude this
(I know there are changes coming but don't quite remember what they
are), an interesting couple of cases are:
$extra_opts = { $ssl => true, ... }
I assume you mean {ssl => true, ...}, and not the value of a variable $ssl ?
apache::vhost { ...
ssl => undef,
attributes => $extra_opts,
}
And:
$extra_opts = { $ssl => undef, ... }
apache::vhost { ...
ssl => true,
attributes => $extra_opts,
}
Both of these results in an error, you are not allowed to set ssl twice
(most likely a mistake).
My expectation is that in both cases 'undef' means "pretend I've said
nothing about thus attribute here" and that *true* wins in either case.
undef only has a special meaning when it is the final value of the given
attribute; it then means "No value specified for this parameter".
That is undef behaves as a "value" until the resource creation takes place.
But what if what is intended is to explicitly *ignore* the setting in
$extra_opts, so that the type's default is used, as if the attribute had
been mentioned by neither the $extra_opts hash or the apache::vhost
declaration? I guess using a hash operation to copy and filter
$extra_opts would do it.
Yes, that is the way to go. In feature parser it is also very easy to
create a new hash where one or several keys are removed. Like this:
$a = { a=> 10, b => 20, c => 30}
$b = $a - [a, b] # $b is set to {c => 30 }
By the way (since the paint's not dry) I think just *attributes* as the
afforementioned metaparam would be best -- it clearly says what it is,
is short, and is meta-sounding enough that I would not even consider
using it "in the field" -- when developing a class, defined type,
type/provider, etc.
Another alternative that occurs to me that breaks the "key => val"
layout and so is cognitively distinct is to use something like the
facilities that many modern languages have for passing hashes or arrays
as arguments to methods/functions:
apache::vhost { $title:
...
**$extra_opts
}
or:
apache::vhost { $title:
...
&$extra_opts
}
or:
apache::vhost { $tilte:
...
*$extra_opts
}
So, that was the initial proposal '*' for any name followed by => and
the value. This also looks similar to the unary splat '*' that can be
used to unfold an array or hash.
That suggestion was not well liked... "no more operators please...".
It would be possible to specify '*' as signaling "here is an attributes
hash". The only quirk is that it would be a special syntactic marker
that is followed by any expression (which includes splat) - no harm,
just slightly odd that you are allowed to write **$extra_opts, where
this is not allowed elsewhere (splat is non associative, just like unary
minus).
- henrik
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