ProgramMemory: avoid unnecessary copy in erase_if()

Author: firewave

lib/programmemory.cpp

@@ -173,14 +173,15 @@ void ProgramMemory::erase_if(const std::function<bool(const ExprIdToken&)>& pred
     if (mValues->empty())
         return;
 
-    // TODO: how to delay until we actuallly modify?
-    copyOnWrite();
+    // TODO: messes with the use count
+    const auto values = mValues;
+
+    for (auto it = values->begin(); it != values->end(); ++it) {
+        if (!pred(it->first))
+            continue;
 
-    for (auto it = mValues->begin(); it != mValues->end();) {
-        if (pred(it->first))
-            it = mValues->erase(it);
-        else
-            ++it;
+        copyOnWrite();
+        mValues->erase(it->first);
     }
 }