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copied!<p>The concept of 'const' is useful to indicate that an object's internal state should not be modifiable.</p> <pre><code>void f(const Object& o) { // 'o' cannot be modified } </code></pre> <p>The ability to mark a non-static member as <code>const</code> allows you to enforce that holders of a <code>const</code> reference to the object cannot modify the internal state. For example, in the following scenario, <code>Object</code> has an accessor <code>str</code> that returns a reference to a internal state, which has both non-const and const overloads:</p> <pre><code>struct Object { // non-const: caller can modify internal state std::string& str(); // const: caller cannot modify internal state const std::string& str() const; }; </code></pre> <p>The non-const overload allows modification of internal state, but can be called only on a non-const reference to the object; the const overload does not allow modification of internal state and can be used with both const and non-const object references.</p> <p>In the scenario you present, <code>Game</code> appears to be a monolithic <a href="http://en.wikipedia.org/wiki/Singleton_pattern" rel="nofollow">singleton</a> object that contains everything in your program. If so, it seems questionable that it would be useful to ever pass a reference to a <code>Game</code> - or to an object derived from it - making the distinction between <code>const Game&</code> and <code>Game&</code> somewhat moot. If this is the case, const-correctness has no utility and you will save yourself a headache if you simply make all members of <code>Game</code> non-const.</p>

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