Description:
------------
Currently it is hard to get to know the exact context from which a method is called from. Sure, there is debug_backtrace and the Reflection API, but these are no ideal nor complete and reliable solutions.

I suggest to introduce a new function: get_calling_context (similar to get_calling_class).

A possible use-case is shown below

Possible return values could be:

<?php
const PHP_CONTEXT_PRIVATE = ?, // Method was called from the class it is defined in.
      PHP_CONTEXT_INHERITED = ?, // Method was called from a class inheriting the defining class.
      PHP_CONTEXT_EXTERN_USER = ?, // Method was called from outside the class, but in userland code
      PHP_CONTEXT_EXTERN_CORE = ?; // Method was called from outside, but was used as callback (Session handler, error handler, any predefined function awaiting a callback
?>

Use case:
Currently I use virtual properties (via __get and __set) to validate and manipulate properties data while still keeping the ability to iterate over the entire object(implementing IteratorAggregate). This allows me also to have different visibility states for accessors (which will hopefully be supported in 5.5 without having to rely on custom implementations) but not for the properties themself.

Simplified __set implementation:
<?php
    public function __set($name, $value)
    {
        // called from wrong context
        if (\property_exists($this, $name)) {
            if (\method_exists($this, 'set' . \ucfirst($name))) {
                return $this->{'set' . \ucfirst($name)}($value);
            } else {
                throw new WritePropertyFromWrongContextException("virtual property $name can not be accessed from this context");
            }
        } elseif (\method_exists($this, 'set' . \ucfirst($name))) {
            return $this->{'set' . \ucfirst($name)}($value);
        } elseif ($this->objectConfiguration['accessMapAsProps'] == true && $this->offsetExists($name)) {
            $this[$name] = $this->createPropertyValidator($name)->validate($value,$this->getRuleSet()[$name])->getValidatedValue();
        } else {
            throw new WriteNonExistingPropertyException("Virtual property \$$name does not exist in class " .
                \get_class($this));
        }
    }
?>

There is no possibility to react on different scenarios as there can be only one __set which is either public,protected or private. There is no option to implement different behaviors for different visibility.

Another usecase is the usage of object callbacks in handlers like session.set.save.handler

For example the write callback does not (per documentation) output data. However in debug scenarios and in unit-tests it would be ideal to know if the method was called from the core as a usual session handler or in a different scenario in usercode.


Additionally this would go inline with already existing functions like get_called_class, get_parent_class and partly get_class.