ReferenceHelper Class Reference

helper class to manage variable references passed to functions and class methods, stack only, cannot be dynamically allocated More...

#include <ReferenceHelper.h>

List of all members.

Public Member Functions

DLLEXPORT ReferenceHelper (const ReferenceNode *ref, AutoVLock &vl, ExceptionSink *xsink)
 initializes the object and tries to get the pointer to the pointer of the lvalue expression target
DLLEXPORT ~ReferenceHelper ()
 destroys the object
DLLLOCAL operator bool () const
 returns true if the reference is valid, false if not
DLLLOCAL qore_type_t getType () const
 returns the type of the reference's value
DLLEXPORT AbstractQoreNodegetUnique (ExceptionSink *xsink)
 returns a pointer to the value with a unique reference count (so it can be updated in place), assumes the reference is valid
DLLEXPORT int assign (AbstractQoreNode *val, ExceptionSink *xsink)
 assigns a value to the reference, assumes the reference is valid
DLLEXPORT const AbstractQoreNodegetValue () const
 returns a constant pointer to the reference's value
DLLEXPORT void swap (ReferenceHelper &other)
 swaps the values of two references

Protected Attributes

AbstractQoreNode ** vp
 pointer to the pointer to the lvalue expression target of the reference


Detailed Description

helper class to manage variable references passed to functions and class methods, stack only, cannot be dynamically allocated

Takes care of safely accessing ReferenceNode objects, for example when they are passed as arguments to a builtin function or method. Locks are automatically acquired in the constructor if necessary and released in the destructor. The constructor could raise a Qore-language exception if there is a deadlock acquiring any locks to access the ReferenceNode's value as given by the lvalue expression, so the object should be checked for this state right after the constructor as in the following example:

    const AbstractQoreNode *p = get_param(params, 0);   
    if (p && p->getType() == NT_REFERENCE) {
       const ReferenceNode *r = reinterpret_cast<const ReferenceNode *>(p);
       AutoVLock vl;
       ReferenceHelper ref(r, vl, xsink);
       // a deadlock exception occurred accessing the reference's value pointer
       if (!ref)
          return 0;

       // more code to access the reference
    }

Constructor & Destructor Documentation

DLLEXPORT ReferenceHelper::ReferenceHelper ( const ReferenceNode ref,
AutoVLock vl,
ExceptionSink xsink 
)

initializes the object and tries to get the pointer to the pointer of the lvalue expression target

Parameters:
ref the ReferenceNode to use
vl the reference to the AutoVLock structure for managing nested locks
xsink Qore-language exceptions raised will be added here (for example, a deadlock accessing the object)


Member Function Documentation

DLLEXPORT int ReferenceHelper::assign ( AbstractQoreNode val,
ExceptionSink xsink 
)

assigns a value to the reference, assumes the reference is valid

Parameters:
val the value to assign (must be already referenced for the assignment)
xsink required for the call to AbstractQoreNode::deref() of the current value
Returns:
0 if there was no error and the variable was assigned, -1 if a Qore-language exception occured dereferencing the current value, in this case no assignment was made and the reference count for val is dereferenced automatically by the ReferenceHelper object
Note:
you must check that the reference is valid before calling this function
          AutoVLock vl;
          ReferenceHelper rh(ref, vl, xsink);
          // if the reference is not valid, then return
          if (!rh)  
             return;
          // make the assignment (if the assignment fails, the value will be dereferenced automatically)
          rh.assign(val->refSelf(), xsink);

DLLLOCAL qore_type_t ReferenceHelper::getType (  )  const [inline]

returns the type of the reference's value

Returns:
the type of the reference's value

References AbstractQoreNode::getType(), NT_NOTHING, and vp.

DLLEXPORT AbstractQoreNode* ReferenceHelper::getUnique ( ExceptionSink xsink  ) 

returns a pointer to the value with a unique reference count (so it can be updated in place), assumes the reference is valid

Parameters:
xsink required for the call to AbstractQoreNode::deref()
Returns:
a pointer to the reference's value with a unique reference count (so it can be modified), or 0 if the value was 0 to start with or if a Qore-language exception was raised
Note:
you must check that the reference is valid before calling this function

take care to only call this function on types where the AbstractQoreNode::realCopy() function has a valid implementation (on all value types suitable for in-place modification this function has a valid implementation), as in debugging builds other types will abort(); in non-debugging builds this function will simply do nothing

          AutoVLock vl;
          ReferenceHelper rh(ref, vl, xsink);
          // if the reference is not valid, then return
          if (!rh)  
             return;
          // get the unique value
          AbstractQoreNode *val = rh.getUnique(xsink);
          // if a Qore-language exception was raised, then return
          if (*xsink)
              return;

DLLEXPORT const AbstractQoreNode* ReferenceHelper::getValue (  )  const

returns a constant pointer to the reference's value

Returns:
the value of the lvalue reference (may be 0)

DLLLOCAL ReferenceHelper::operator bool (  )  const [inline]

returns true if the reference is valid, false if not

false will only be returned if a Qore-language exception was raised in the constructor

References vp.


The documentation for this class was generated from the following file:

doxygen