D 2018-07-03T21:09:21.905
L config
N text/x-markdown
P e1ad60618e01c55443a5b88263446b4d1510cc777e0ddeff326728dcc81cd571
U mario
W 4309
## # config:  {…}

The `config:` field is a list of entries describing feature- and
application-level settings.

    # config:
    #    { name: linky, type: bool, description: autolink urls }
    #    { name: xy.title, type: str, value: "blog title" }
    #    { name: perm, type: select, select: 3=USER|2=EX|1=SUP|0=KERN }

[PMD](wiki/Plugin+Meta+Data) is about uniform feature lookup. And
plugin handling goes hand in hand with configuration management.
However it requires a structured field to avoid bulky definitions, yet
support enough variation.

Usually `config:` contains multiple indented lines, each being a
<acronym title="JSON, but quotes optional">JSOL</acronym>-dictionary.

#### {

<style>
 .cnt-tbl { background: #fcfcfc; }
 .cnt-tbl th { vertical-align: top; text-align: left; }
 .cnt-tbl td, .cnt-tbl th { padding: 7pt; border: 2px solid #f3f3f3; }
</style>
<table class="cnt-tbl">
<tr>
   <th><code>name:</code></th>
   <td>associates some variable/constant/expression to a setting.</td>
</tr>
<tr>
<th><code>type:</code></th>
<td> A few common types may cover 90% of configuration needs.
   <table>
    <tr>
       <th><code>bool</code>/<code>boolean</code></th>
       <td>would render as checkbox often.</td>
    </tr>
    <tr>
       <th><code>str</code>/<code>string</code></th>
       <td>for plain textual content.</td>
    </tr>
    <tr>
       <th><code>int</code>/<code>integer</code></th>
       <td>verifies the value to be numeric.</td>
    </tr>
    <tr>
       <th><code>select</code>/<code>multi</code></th>
       <td> defining a predefined list of defaults.</td>
    </tr>
   </table>
</td>
</tr>
<tr>
    <th><code>select:</code></tt>
      <td>* With `select: "aaa┃bbb┃ccc"` being the alternatives attribute for
    combobox options.</td>
</tr>
<tr>
    <th><code>description:</code></th>
    <td>holds some elaboration on the key name.</td>
</tr>
<tr>
    <th><code>value:</code></th>
   <td>just sets a default</td>
</tr>
</table>

#### }

## Storage and key `name:`

Notably this scheme just defines a list of available options. It does **not**
prescribe if they're stored in an `.ini`, `.json`, `xml` or code file, or a database
perhaps.  
Applications might utilize different stores even, and dispatch depending on
the `name:` syntax

  * For example `name: ALL_UPPERCASE` might become a code constant,
  * While `name: sectioned.feature.option` indicated an INI setting,
  * Or `name: "$cfg.plugins[after][]"` even a literal code target.

So names can be somewhat free-form. I'd avoid including the `$` sigil
however, or spaces obviously. Mostly-alphunumeric and dotted keys are
certainly most versatile.


## `select:` type and alternatives

The syntax for `select:` is

 * preferrably `"alt|alt|alt"`
 * or with optional title `"1=title|2=alternative|3=…"`.
 * Though implementations may allow to use `,` comma and `|` dash.
 * Or `:` like `=` again.


## Other fields and types

Other per-config attributes migh encompass

 * `category:` and `class:` for decoration or grouping.
 * Or `arg:` and `param:` for defining commandline args rather than global application settings.

Other types might be

 * `text` for lengthy textarea-style strings),
 * `color` for a color picker,
 * `file` bringing up a file selection dialog
 * Or `table`/`csv`/`dict` for supporting more complex (Excel-style) setting lists.


## Regex tokenizer

You can get by with a somewhat simple regex extractor for this config
scheme. It's simply finding `{…}` pairs, then splitting key-value pairs,
and handling optional quoting.

  * Which allows syntax alternatives `[:=>]+` for key-value pairs.

  * Same as shortened/aliased type names add some user-friendliness.

Of course a stringent JSON-parser could be used. But that's obstructing
maintanability, and buys little performance-wise. (Plugin or option
management is rarely done during runtime; but confined to some admin
or installer UI.)


## Purpose

Once config options are easily parseable, it quickly pays off to implement
a centralized option/admin UI. And it sometimes can be combined with plugin
configuration itself. Which is why plugin meta data defines this simple
scheme.


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