map with const keys but non const values?

Question

I have a situation, where I would like to have a map that does not allow to add/remove keys after initialization, but the values are allowed to change (thus I cannot simply

Answer 1

I see 2 options here

1. Make the map const and use const_cast when changing something

   const std::map myMap;

   myMap[1] = 2; // NOT OK, because const map

   (const_cast&>(myMap)).at(1) = 2; // OK with const_cast

2. make an wrapper class or derive an custom map that has only read and update existing value methods

I don't think there is an built in way to make an map only with update value, and restrict and insert.