Multi-operand constructor for code_ifthenelset

This enables RAII rather then incremental construction.

Author: tautschnig

src/util/std_code.h

@@ -583,6 +583,25 @@ class code_ifthenelset:public codet
     op2().make_nil();
   }
 
+  /// An if \p condition then \p then_code else \p else_code statement.
+  code_ifthenelset(
+    const exprt &condition,
+    const codet &then_code,
+    const codet &else_code)
+    : codet(ID_ifthenelse)
+  {
+    add_to_operands(condition, then_code, else_code);
+  }
+
+  /// An if \p condition then \p then_code statement (no "else" case).
+  code_ifthenelset(
+    const exprt &condition,
+    const codet &then_code)
+    : codet(ID_ifthenelse)
+  {
+    add_to_operands(condition, then_code, nil_exprt());
+  }
+
   const exprt &cond() const
   {
     return op0();