Improve class_typet's base description

This defines an exprt subclass representing a base class instead of
using a bare exprt, and enforces proper types when returning the base
list. It's the same shape as the existing exprt so old code doesn't need
adjusting, it just makes client code neater.

Author: smowton

src/cegis/cegis-util/type_helper.cpp

@@ -34,10 +34,10 @@ bool instanceof(const typet &lhs, const typet &rhs, const namespacet &ns)
   if (type_eq(lhs, rhs, ns)) return true;
   assert(ID_class == lhs.id());
   const class_typet &lhs_class=to_class_type(lhs);
-  const irept::subt &bases=lhs_class.bases();
-  for (const irept &base : bases)
+  const class_typet::basest &bases=lhs_class.bases();
+  for(const exprt &base : bases)
   {
-    const typet &type=static_cast<const typet &>(base.find(ID_type));
+    const typet &type=base.type();
     if (instanceof(ns.follow(type), rhs, ns)) return true;
   }
   return false;

src/util/std_types.h

@@ -361,31 +361,40 @@ class class_typet:public struct_typet
     return is_class()?ID_private:ID_public;
   }
 
-  const irept::subt &bases() const
+  class baset:public exprt
   {
-    return find(ID_bases).get_sub();
+  public:
+    baset():exprt(ID_base)
+    {
+    }
+
+    explicit baset(const typet &base):exprt(ID_base, base)
+    {
+    }
+  };
+
+  typedef std::vector<baset> basest;
+
+  const basest &bases() const
+  {
+    return (const basest &)find(ID_bases).get_sub();
   }
 
-  irept::subt &bases()
+  basest &bases()
   {
-    return add(ID_bases).get_sub();
+    return (basest &)add(ID_bases).get_sub();
   }
 
   void add_base(const typet &base)
   {
-    bases().push_back(exprt(ID_base, base));
+    bases().push_back(baset(base));
   }
 
   bool has_base(const irep_idt &id) const
   {
-    const irept::subt &b=bases();
-
-    forall_irep(it, b)
+    for(const auto &b : bases())
     {
-      assert(it->id()==ID_base);
-      const irept &type=it->find(ID_type);
-      assert(type.id()==ID_symbol);
-      if(type.get(ID_identifier)==id)
+      if(to_symbol_type(b.type()).get(ID_identifier)==id)
         return true;
     }