Add few clarifying comments

2 files changed, 5 insertions, 2 deletions

diff --git a/build2/variable.cxx b/build2/variable.cxx
index 8d9aa14..ce88712 100644
--- a/build2/variable.cxx
+++ b/build2/variable.cxx
@@ -1135,7 +1135,7 @@ namespace build2
 
     variable& r (p.first->second);
 
-    if (!p.second)
+    if (!p.second) // Note: overridden variable will always exist.
     {
       if (t != nullptr || v != nullptr || o != nullptr)
         update (r, t, v, o); // Not changing the key.
diff --git a/build2/variable.hxx b/build2/variable.hxx
index 60a1699..c5e1a13 100644
--- a/build2/variable.hxx
+++ b/build2/variable.hxx
@@ -117,6 +117,9 @@ namespace build2
   // reset() before any other variables. Project wide overrides are entered in
   // main(). Overriding happens in scope::find_override().
   //
+  // NULL type and normal visibility are the defaults and can be overridden by
+  // "tighter" values.
+  //
   struct variable
   {
     string name;
@@ -804,7 +807,7 @@ namespace build2
   class variable_pool
   {
   public:
-    // Find existing or insert new.
+    // Find existing (assert exists).
     //
     const variable&
     operator[] (const string& name) const;