Uniformly treat NULL pointers to incremental expressions as incremental expressions that are always "true".

I considered trying to optimize by stripping NULLs out of "and" and
"or" expressions, but that seems a bit tricky.  It might be more
straightforward if I introduce "true" and "false" expressions
explicitly, though (part of the trouble is that it's probably bad if
creation routines return NULL, and they can't currently return false).

1 files changed, 9 insertions, 5 deletions

diff --git a/src/generic/problemresolver/incremental_expression.cc b/src/generic/problemresolver/incremental_expression.cc
index 8f5c1547..7285cefc 100644
--- a/src/generic/problemresolver/incremental_expression.cc
+++ b/src/generic/problemresolver/incremental_expression.cc
@@ -1,7 +1,7 @@
 /** \file incremental_expression.cc */   // -*-c++-*-
 
 
-//   Copyright (C) 2009 Daniel Burrows
+//   Copyright (C) 2009-2010 Daniel Burrows
 //
 //   This program is free software; you can redistribute it and/or
 //   modify it under the terms of the GNU General Public License as
@@ -27,7 +27,7 @@ void counting_bool_e::init_num_true()
   num_true = 0;
   for(std::vector<cwidget::util::ref_ptr<expression<bool> > >::const_iterator
 	it = children.begin(); it != children.end(); ++it)
-    if((*it)->get_value())
+    if(!it->valid() || (*it)->get_value())
       ++num_true;
 }
 
@@ -53,7 +53,7 @@ void counting_bool_e::child_modified(const cwidget::util::ref_ptr<expression<boo
 
 void counting_bool_e::add_child(const cwidget::util::ref_ptr<expression<bool> > &child)
 {
-  if(child->get_value())
+  if(!child.valid() || child->get_value())
     {
       bool old_value = get_value();
 
@@ -71,7 +71,7 @@ void counting_bool_e::add_child(const cwidget::util::ref_ptr<expression<bool> >
 
 void counting_bool_e::remove_child(const cwidget::util::ref_ptr<expression<bool> > &child)
 {
-  if(child->get_value())
+  if(!child.valid() || child->get_value())
     {
       bool old_value = get_value();
 
@@ -116,7 +116,11 @@ void not_e::child_modified(const cwidget::util::ref_ptr<expression<bool> > &chil
 
 bool not_e::get_value()
 {
-  return !get_child()->get_value();
+  if(get_child().valid())
+    return !get_child()->get_value();
+  else
+    // NULL pointers count as "true".
+    return false;
 }
 
 void not_e::dump(std::ostream &out)