improved typing in simplify_boolean

This improves type safety.

Author: Daniel Kroening

src/util/simplify_expr_boolean.cpp

@@ -27,17 +27,17 @@ simplify_exprt::resultt<> simplify_exprt::simplify_boolean(const exprt &expr)
 
   if(expr.id()==ID_implies)
   {
-    if(
-      expr.operands().size() != 2 ||
-      expr.operands().front().type().id() != ID_bool ||
-      expr.operands().back().type().id() != ID_bool)
+    const auto &implies_expr = to_implies_expr(expr);
+
+    if(implies_expr.op0().type().id() != ID_bool ||
+       implies_expr.op1().type().id() != ID_bool)
     {
       return unchanged(expr);
     }
 
     // turn a => b into !a || b
 
-    auto new_expr = expr;
+    binary_exprt new_expr = implies_expr;
     new_expr.id(ID_or);
     new_expr.op0() = boolean_negate(new_expr.op0());
     simplify_node(new_expr);