Add support for getting components by name to struct_exprt

Author: thomasspriggs

src/util/std_expr.h

@@ -1823,6 +1823,24 @@ class struct_exprt:public exprt
     exprt(ID_struct, _type)
   {
   }
+
+  /// \return The expression for a named component of this struct.
+  exprt &component(const irep_idt &name)
+  {
+    const auto index = to_struct_type(type()).component_number(name);
+    DATA_INVARIANT(
+      index < operands().size(), "component matching index should exist");
+    return operands()[index];
+  }
+
+  /// \return The expression for a named component of this struct.
+  const exprt &component(const irep_idt &name) const
+  {
+    const auto index = to_struct_type(type()).component_number(name);
+    DATA_INVARIANT(
+      index < operands().size(), "component matching index should exist");
+    return operands()[index];
+  }
 };
 
 /*! \brief Cast a generic exprt to a \ref struct_exprt