README

What's This?

A small library to provide strictly typed access to data in an array, intended for use with a nested array of application configuration data. Nested values are dereferenced with dotted strings.

Usage

Install

Install this package with composer:

composer require timdev/typed-config

Usage

In a nutshell:

declare(strict_types=1);

// This should already be set in your php.ini, but this library depends on it,
// so you should verify that's set.
ini_set('assert.exception', 1);

// Could come from anywhere.
$configArray = [
    'myapp' => [
        'some-api' => [
            'baseUrl' => 'https://example.com/v1/',
            'timeout' => 30
        ],
        'allowed_ips' => [
            '192.168.0.1',
            '192.168.0.50'
        ],
        'optional_value' => null        
    ]
];

$config = new Config($configArray);

// Methods have narrow return type declarations:
$baseUrl = $config->string('myapp.some-api.baseUrl');
$timeout = $config->int('myapp.some-api.timeout');
$allowed = $config->list('myapp.allowed_ips');

// Attempting to access an undefined value throws.
$port = $config->int('invalid.key');  // Throws \TimDev\TypedConfig\Exception\KeyNotFound

// Note that the main methods do not have nulalble return types.
$optional = $config->bool('myapp.optional_value'); // Also throws!

// Use ->nullable to access valeus that are defined, but might be null:
$optional = $config->nullable->bool('myapp.optional_value'); 

Assumptions and Design

In order to use this library effectively, it's important to understand its design and the assumptions that inform that design.

Assumption: All valid configuration values are defined

As demonstrated in example above, client code attempting to access an undefined value will throw. Our opinion is that a library or application should ship a complete default configuration. This is always a win for users. This design means that users are alerted early when they try to access an invalid key due to a typo or transcription error.

If you think you need an optional configuration parameter, you should instead provide a default such as null or perhaps [].

Design: Relies on PHP's assert()

assert is a language construct with a very useful mechanism: they are optimized out in production. This library uses assert() to type-check your configuration values before they're returned from the various accessor-methods.

If you're unfamiliar with the configuration values that affect how assert works, you should review the documentation and your environment's configuration before using this library. The short version is that you'll want to ensure that assert.exception = 1 and zend.assertion = 1 in your development and testing environments.

Because this library depends on assert(), the type checks are optimized away in production environments (where zend.assertion = 0). This reduces some overhead but means that configuration access that would throw an AssertionError in development will instead:

1. Throw a TypeError, or
2. Not throw anything, in the case of a hash/list mismatch.

Motivation

We developed this while building an application with mezzio, where configuration data are generally pulled from an array. Arrays are nice, but often cause you to have to:

1. Code defensively whenever you pull some value from your $config array.
2. Add assertions or comments to let your static analyzer of choice figure out what is happening.

This library is an attempt to improve that situation.

Alternatives

There are other libraries that approach the problem from different perspectives.

selective-php/config takes a similar approach in that it provides strictly typed methods to fetch (possibly nullable) values. Unlike this library, it enforces types by casting values as it returns them. We take a more strict posture, and consider mismatched types to be an error in the software. Its nullable-typed methods return null if a config key is not defined, while we consider that to be an error as well.

setbased/typed-config is also similar. Like the previously discussed library, it will attempt to cast whatever it finds in the config data to the required type, and is more permissive about undefined config keys than this library is.

league/config takes an even more strict approach by helping you define a strict schema for your configuration data. We really like that approach (at least for some contexts), but are somewhat bewildered that it provides a single get(string $key): mixed accessor.

To Do

• Do some benchmarks and determine if our usage of assert is actually providing any tangible benefit.