PHP RFC: isReadable/Writeable reflection methods

• Version: 0.9
• Date: 2024-11-28
• Author: Ilija Tovilo (tovilo.ilija@gmail.com), Larry Garfield (larry@garfieldtech.com)
• Status: Draft
• First Published at: http://wiki.php.net/rfc/isreadable-iswriteable
• Pull Request: https://github.com/php/php-src/pull/16209

The ReflectionProperty::isPublic() method, by design, indicates only if a property has a “public” flag set on it, nothing more. Prior to PHP 8.1, that implicitly also meant “can be written to from scope outside the object.” However, PHP 8.1 introduced readonly properties, which broke that assumption with implicit private-set visibility. The addition of explicit asymmetric visibility in PHP 8.4 further undermined that assumption. The result is that there is currently no straightforward way to determine at runtime if reading from or writing to a property would be allowed. This RFC attempts to provide such a utility.

The ReflectionProperty object will be expanded with two additional methods, as defined below:

class ReflectionProperty
{
    // ... All the existing functionality.
 
    public function isReadable(?string $scope = 'static', ?object $object = null): bool {}
 
    public function isWriteable(?string $scope = 'static', ?object $object = null): bool {}
}

The behavior of the parameters is the same for both methods.

The $scope parameter specifies the scope from which we want to know if the operation is valid. Put another way, these methods can be read as “if I were to try to read/write this property from $scope, would that be allowed?”

The $scope parameter may have one of three values:

• The string static. This is the default if no scope is specified. This indicates the desired scope is wherever the method is being called from. It means essentially “if the code right after this method call tried to read/write the property, is that allowed?”
• null. A null scope refers to the global scope. That is, “would it be allowed to read/write this property from global scope?”
• A class name string. Any defined class name. “Would it be allowed to read/write this property from a method on this class?”

The $object parameter is an optional object to analyze the property on. If not provided, the analysis will look only at static information on the property, and thus ignore information such as if a readonly property has already been written to.

Both methods will examine the same information about a property, if available, to determine if the operation would be allowed.

isReadable()

• Checks that the property is readable from the passed scope
• Checks that the property is initialized (i.e. not typed and never written to) (This check is skipped if no $object is provided.)
• Checks that the property is not virtual or has a get hook

isWritable()

• Checks that the property is writable (respecting symmetric and asymmetric properties) from the passed scope
• Checks that the property is not readonly, is not yet initialized, or is reinitializable (__clone) (Initialization is not checked if no $object is provided.)
• Checks that the property is not virtual or has a set hook

Of note, this does not absolutely guarantee that a read/write will succeed. There's at least two exceptions:

One, some PHP built-in classes have effectively immutable properties but do not use readonly or private(set). Those would not be detected here, until and unless they are updated to use the now-available mechanisms. (See, eg: https://github.com/php/php-src/issues/15309)

Two, a get or set hook may throw an exception under arbitrarily complex circumstances. There is no way to evaluate that via reflection, so it's a gap that will necessarily always be there.

The magic methods __get and __set pose an interesting challenge, especially when combined with an unset property. For reading, the presence of a __get method means that any arbitrary property name might be readable, including those that are defined but explicitly unset() (a common trick in the past for lazy initialization before hooks were available). For writing, the presence of a __set method means that any arbitrary property name might be writeable, even if not defined.

In practice, there are only two reasonable ways to address this question.

1. The presence of __get is completely ignored.
2. The presence of __get implies isReadable() will always return true.

(And then the same question for __set, which doesn't have to be answered the same way but probably should be for consistency.)

The authors are open to either approach, depending on what the consensus is. If no consensus is found, we will go with the “ignore” option.

None.

PHP 8.5

Yes or no vote, 2/3 required to pass.

After the project is implemented, this section should contain

1. the version(s) it was merged into
2. a link to the git commit(s)
3. a link to the PHP manual entry for the feature
4. a link to the language specification section (if any)

Links to external references, discussions or RFCs

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