发布于 2015-08-27 16:52:24 | 196 次阅读 | 评论: 0 | 来源: 网络整理
The ExpressionLanguage can be extended by adding custom functions. For instance, in the Symfony Framework, the security has custom functions to check the user’s role.
注解
If you want to learn how to use functions in an expression, read “Working with Functions”.
Functions are registered on each specific ExpressionLanguage instance.
That means the functions can be used in any expression executed by that
instance.
To register a function, use
register().
This method has 3 arguments:
use SymfonyComponentExpressionLanguageExpressionLanguage;
$language = new ExpressionLanguage();
$language->register('lowercase', function ($str) {
return sprintf('(is_string(%1$s) ? strtolower(%1$s) : %1$s)', $str);
}, function ($arguments, $str) {
if (!is_string($str)) {
return $str;
}
return strtolower($str);
});
echo $language->evaluate('lowercase("HELLO")');
This will print hello. Both the compiler and evaluator are passed
an arguments variable as their first argument, which is equal to the
second argument to evaluate() or compile() (e.g. the “values” when
evaluating or the “names” if compiling).
2.6 新版功能: Expression providers were introduced in Symfony 2.6.
When you use the ExpressionLanguage class in your library, you often want
to add custom functions. To do so, you can create a new expression provider by
creating a class that implements
ExpressionFunctionProviderInterface.
This interface requires one method:
getFunctions(),
which returns an array of expression functions (instances of
ExpressionFunction) to
register.
use SymfonyComponentExpressionLanguageExpressionFunction;
use SymfonyComponentExpressionLanguageExpressionFunctionProviderInterface;
class StringExpressionLanguageProvider implements ExpressionFunctionProviderInterface
{
public function getFunctions()
{
return array(
new ExpressionFunction('lowercase', function ($str) {
return sprintf('(is_string(%1$s) ? strtolower(%1$s) : %1$s)', $str);
}, function ($arguments, $str) {
if (!is_string($str)) {
return $str;
}
return strtolower($str);
}),
);
}
}
You can register providers using
registerProvider()
or by using the second argument of the constructor:
use SymfonyComponentExpressionLanguageExpressionLanguage;
// using the constructor
$language = new ExpressionLanguage(null, array(
new StringExpressionLanguageProvider(),
// ...
));
// using registerProvider()
$language->registerProvider(new StringExpressionLanguageProvider());
小技巧
It is recommended to create your own ExpressionLanguage class in your
library. Now you can add the extension by overriding the constructor:
use SymfonyComponentExpressionLanguageExpressionLanguage as BaseExpressionLanguage;
use SymfonyComponentExpressionLanguageParserCacheParserCacheInterface;
class ExpressionLanguage extends BaseExpressionLanguage
{
public function __construct(ParserCacheInterface $parser = null, array $providers = array())
{
// prepend the default provider to let users override it easily
array_unshift($providers, new StringExpressionLanguageProvider());
parent::__construct($parser, $providers);
}
}