Contexts

[MGatner]

This PR expands the core function to add a new feature: contexts. A "contextual setting" is a way of defining a setting for a specific subset of circumstances, left to the developer to define (see #15 (comment)). Contextual settings fall back on their "global" version (i.e. the current behavior), providing one more layer of customizability. An example of a contextual setting might be environment-specific URLs:

service('Settings')->set('App.homepage', '/welcome', 'environment:production');
service('Settings')->set('App.homepage', '/debug', 'environment:development');

In order to facilitate detection of "hits" versus "misses" this PR also adds the has() method to handlers to determine whether a value is present or not. This expands on null value support, since we can now differentiate between "nonexistent" and "present but null".

Note: Because this feature modifies an abstract method definition it will require a major release.

[MGatner]

The BC check failure is expected, as noted.

[lonnieezell]

I think our hydration system and caching system will need to change. If we have thousands of users in the system we don't want to load all of their individual settings into the system at once. I would recommend that hydrate could take the $context. If present it caches it locally under the context name, otherwise keeps another cache for non-context settings.

private $settings = [
   'general' => [],
   'contexts' => []
];

[MGatner]

Good idea!

[sfadschm]

If I define a contraint that does not match, but have a default value defined in a config file, will settings fallback to the config or null?

On the same note:
If I define a setting twice, once with and once without constraint, then I guess it will fallback to the contraint-less value if not matching, right?

[MGatner]

That's correct. It is a cascading check, so if you supply a context then the return is "setting with context > setting without context > Config value > null".

I tried to make this clear in the README:

If that context is not found the library falls back to the global value, i.e. service('setting')->get('App.theme')

@sfadschm Did you miss that, or did you read that and still found it confusing?

[sfadschm]

Did you miss that, or did you read that and still found it confusing?

Miss...
However, I like the phrasing in your answer. Maybe explicitly stating the cascade chain could be helpful in the docs (although it should in principle be understandable the way it is now).