C++ pANTLR3_BASE_TREE::reuse方法代码示例

/** If oldRoot is a nil root, just copy or move the children to newRoot.
 *  If not a nil root, make oldRoot a child of newRoot.
 *
 * \code
 *    old=^(nil a b c), new=r yields ^(r a b c)
 *    old=^(a b c), new=r yields ^(r ^(a b c))
 * \endcode
 *
 *  If newRoot is a nil-rooted single child tree, use the single
 *  child as the new root node.
 *
 * \code
 *    old=^(nil a b c), new=^(nil r) yields ^(r a b c)
 *    old=^(a b c), new=^(nil r) yields ^(r ^(a b c))
 * \endcode
 *
 *  If oldRoot was null, it's ok, just return newRoot (even if isNilNode).
 *
 * \code
 *    old=null, new=r yields r
 *    old=null, new=^(nil r) yields ^(nil r)
 * \endcode
 *
 *  Return newRoot.  Throw an exception if newRoot is not a
 *  simple node or nil root with a single child node--it must be a root
 *  node.  If newRoot is <code>^(nil x)</endcode> return x as newRoot.
 *
 *  Be advised that it's ok for newRoot to point at oldRoot's
 *  children; i.e., you don't have to copy the list.  We are
 *  constructing these nodes so we should have this control for
 *  efficiency.
 */
static	pANTLR3_BASE_TREE	
becomeRoot	(pANTLR3_BASE_TREE_ADAPTOR adaptor, pANTLR3_BASE_TREE newRootTree, pANTLR3_BASE_TREE oldRootTree)
{
    pANTLR3_BASE_TREE saveRoot;

	/* Protect against tree rewrites if we are in some sort of error
	 * state, but have tried to recover. In C we can end up with a null pointer
	 * for a tree that was not produced.
	 */
	if	(newRootTree == NULL)
	{
		return	oldRootTree;
	}

	/* root is just the new tree as is if there is no
	 * current root tree.
	 */
	if	(oldRootTree == NULL)
	{
		return	newRootTree;
	}

	/* Produce ^(nil real-node)
	 */
	if	(newRootTree->isNilNode(newRootTree))
	{
		if	(newRootTree->getChildCount(newRootTree) > 1)
		{
			/* TODO: Handle tree exceptions 
			 */
			ANTLR3_FPRINTF(stderr, "More than one node as root! TODO: Create tree exception handling\n");
			return newRootTree;
		}

		/* The new root is the first child, keep track of the original newRoot
         * because if it was a Nil Node, then we can reuse it now.
		 */
        saveRoot    = newRootTree;
		newRootTree = (pANTLR3_BASE_TREE)newRootTree->getChild(newRootTree, 0);

        // Reclaim the old nilNode()
        //
        saveRoot->reuse(saveRoot);
	}

	/* Add old root into new root. addChild takes care of the case where oldRoot
	 * is a flat list (nill rooted tree). All children of oldroot are added to
	 * new root.
	 */
	newRootTree->addChild(newRootTree, oldRootTree);

    // If the oldroot tree was a nil node, then we know at this point
    // it has become orphaned by the rewrite logic, so we tell it to do
    // whatever it needs to do to be reused.
    //
    if  (oldRootTree->isNilNode(oldRootTree))
    {
        // We have taken an old Root Tree and appended all its children to the new
        // root. In addition though it was a nil node, which means the generated code
        // will not reuse it again, so we will reclaim it here. First we want to zero out
        // any pointers it was carrying around. We are just the baseTree handler so we
        // don't know necessarilly know how to do this for the real node, we just ask the tree itself
        // to do it.
        //
        oldRootTree->reuse(oldRootTree);
    }
	/* Always returns new root structure
	 */
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