Given a data source representing key => value pairs, resolve placeholders like ${foo.bar} to the value associated with the foo.bar key in the data source.

Placeholder Resolver is intended to be used at a relatively low level. For example, a configuration library could use Placeholder Resolver behind the scenes to allow for configuration values to reference other configuration values.

conn.driver: mysql
conn.db_name: example
conn.hostname: 127.0.0.1
conn.username: root
conn.password: pa$$word

Given the appropriate DataSourceInterface implementation to provide the above data as a set of key => value pairs, the Placeholder Resolver would resolve the value of $dsnPattern to mysql:dbname=example;host=127.0.0.1.

$dsnPattern = '${conn.driver}:dbname=${conn.db_name};host=${conn.hostname}';
$dsn = $placeholderResolver->resolveValue($dsnPattern);
// mysql:dbname=example;host=127.0.0.1

• PHP 5.3+

use Dflydev\PlaceholderResolver\RegexPlaceholderResolver;

// YourDataSource implements Dflydev\PlaceholderResolver\DataSource\DataSourceInterface
$dataSource = new YourDataSource;

// Create the placeholder resolver
$placeholderResolver = new RegexPlaceholderResolver($dataSource);

// Start resolving placeholders
$value = $placeholderResolver->resolvePlaceholder('${foo}');

The RegexPlaceholderResolver constructor accepts two additional arguments, a placeholder prefix and a placeholder suffix. The default placeholder prefix is ${ and the default placeholder suffix is }.

To handle placeholders that look like <foo.bar> instead of ${foo.bar}, one would instantiate the class like this:

$placeholderResolver = new RegexPlaceholderResolver($dataSource, '<', '>');

Placeholders can recursively resolve placeholders. For example, given a data source with the following:

array(
    'foo' => 'FOO',
    'bar' => 'BAR',
    'FOO.BAR' => 'BAZ!',
);

The placeholder ${${foo}.${bar}} would internally be resolved to ${FOO.BAR} before being further resolved to BAZ!.

Resolved placeholders are cached using the CacheInterface. The default Cache implementation is used unless it is explicitly set on the Placeholder Resolver.

// YourCache implements Dflydev\PlaceholderResolver\Cache\CacheInterface
$cache = new YourCache;

$placeholderResolver->setCache($cache);

This library is licensed under the New BSD License - see the LICENSE file for details.

If you have questions or want to help out, join us in the #dflydev channel on irc.freenode.net.

Much of the ideas behind this library came from Spring's Property Placeholder Configurer implementation.