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    <p>this is more correct, but not entirely robust:</p> <pre><code>#include &lt;mutex&gt; class A { private: int i; std::mutex mtx; public: A() : i(0), mtx() { } /* this is one option for implementation, but would be rewritten when there are more ivars in order to reduce acquisition counts */ A(A&amp; other) : i(other.get()), mtx() { } ~A() { /* unsafe if subclassed, also useful for determining whether objects are destroyed prematurely (e.g., by their containers */ std::lock_guard&lt;std::mutex&gt; _mylock(this-&gt;mtx); } A&amp; operator=(A&amp; other) { std::lock_guard&lt;std::mutex&gt; _mylock(this-&gt;mtx); std::lock_guard&lt;std::mutex&gt; _otherlock(other.mtx); this-&gt;i = other.i; /* you could call other.get() and bypass the lock_guard, but i'm assuming there's really more work to be done here */ return *this; } int get() { std::lock_guard&lt;std::mutex&gt; _mylock(this-&gt;mtx); return this-&gt;i; } private: /* prohibited */ A(const A&amp; other); /* also prohibited */ A&amp; operator=(const A&amp; other); }; </code></pre>
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    1. POThread-safe copy constructor/assignment operator
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    1. COI do not wish to use the get() function - mainly because it is not generic enough; what happens if I have multiple values (look also at my note)? You are also making two mistakes: your version would deadlock in a self-assignment case and mutex.lock() can throw an exception in your destructor. Finally, I am declaring mutex as mutable, so the const does not create any problems.
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    2. CO@ipapdop re init: you can still initialize correctly with one acquisition if you create an object to pass as an argument. re deadlocks: it's good to create a second template parameter for the type of lock you'll use, or base classes which are lockable. subclasses with locks are often ideal because you'd rather protect the object's vulnerable state, rather than the members within restricted scopes. attempting to ensure thread safety using a basic mutex for an arbitrary `T` is too often tedious and error prone.
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    3. CO(cont) a singular interface (as a generic pattern) is very susceptable to deadlocks (some of which will be intensely difficult to reproduce). your example is trivial in comparison to real world usage; a recursive mutex is more practical generalized object lock. it's also best to write/use a few additional objects to convey and enforce your intentions at every stage within the implementation. using `mutable` will only save you from rewriting existing code today. if thread safety and program correctness is your primary concern, i encourage you to omit it.
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