Introduce ID_pointer_to_member to replace "pointer-to-member" string literals

This is more efficient and avoids bugs caused by typos.

Author: tautschnig

src/cpp/cpp_typecheck_expr.cpp

@@ -53,7 +53,7 @@ void cpp_typecheckt::typecheck_expr_main(exprt &expr)
     typecheck_expr_cpp_name(expr, cpp_typecheck_fargst());
   else if(expr.id()=="cpp-this")
     typecheck_expr_this(expr);
-  else if(expr.id()=="pointer-to-member")
+  else if(expr.id() == ID_pointer_to_member)
     convert_pmop(expr);
   else if(expr.id() == ID_new_object)
   {
@@ -2605,8 +2605,8 @@ void cpp_typecheckt::typecheck_expr_dereference(exprt &expr)
 
 void cpp_typecheckt::convert_pmop(exprt &expr)
 {
-  assert(expr.id()=="pointer-to-member");
-  assert(expr.operands().size() == 2);
+  PRECONDITION(expr.id() == ID_pointer_to_member);
+  PRECONDITION(expr.operands().size() == 2);
 
   if(
     expr.op1().type().id() != ID_pointer ||

src/cpp/parse.cpp

@@ -5377,7 +5377,7 @@ bool Parser::rPmExpr(exprt &exp)
     exprt left;
     left.swap(exp);
 
-    exp=exprt("pointer-to-member");
+    exp = exprt(ID_pointer_to_member);
     exp.move_to_operands(left, right);
     set_location(exp, tk);
   }

src/util/irep_ids.def

@@ -721,6 +721,7 @@ IREP_ID_ONE(throw_decl)
 IREP_ID_ONE(typeid)
 IREP_ID_TWO(C_quoted, #quoted)
 IREP_ID_ONE(to_member)
+IREP_ID_ONE(pointer_to_member)
 
 // Projects depending on this code base that wish to extend the list of
 // available ids should provide a file local_irep_ids.def in their source tree