The following are several English titles that match the content of the article: Concise title (short and direct): * How to Build a Simple ScopeGuard with C 11 Idioms? * Implementing a Simple ScopeGuard in C 11: A Practical Approach * C 11 ScopeGuard: A Concise and Practical I

Concise and practical ScopeGuard in C 11

Question:

How to use C 11 idioms to write based on Alexandrescu concept Simple ScopeGuard?

Answer:

The following is a ScopeGuard implementation based on C 11 idiom:

<code class="cpp">namespace RAII
{
    template
    class ScopeGuard
    {
        mutable bool committed;
        Lambda rollbackLambda; 
        public:

            ScopeGuard( const Lambda& _l) : committed(false) , rollbackLambda(_l) {}

            template
            ScopeGuard( const AdquireLambda& _al , const Lambda& _l) : committed(false) , rollbackLambda(_l)
            {
                _al();
            }

            ~ScopeGuard()
            {
                if (!committed)
                    rollbackLambda();
            }
            inline void commit() const { committed = true; }
    };

    template
    const ScopeGuard& makeScopeGuard( const aLambda& _a , const rLambda& _r)
    {
        return ScopeGuard( _a , _r );
    }

    template<typename rlambda>
    const ScopeGuard& makeScopeGuard(const rLambda& _r)
    {
        return ScopeGuard(_r );
    }
}</typename></code>

Usage:

<code class="cpp">void SomeFuncThatShouldBehaveAtomicallyInCaseOfExceptions() 
{
   std::vector<int> myVec;
   std::vector<int> someOtherVec;

   myVec.push_back(5);
   //first constructor, adquire happens elsewhere
   const auto& a = RAII::makeScopeGuard( [&]() { myVec.pop_back(); } );  

   //sintactically neater, since everything happens in a single line
   const auto& b = RAII::makeScopeGuard( [&]() { someOtherVec.push_back(42); }
                     , [&]() { someOtherVec.pop_back(); } ); 

   b.commit();
   a.commit();
}</int></int></code>

Advantages:

• Simple and easy to use
• Concise code
• Supports exception handling

Potential issues:

• If the advise lambda function throws an exception, the release lambda function is never called because it never fully constructs the ScopeGuard.
• If the cleanup function throws an exception, the program will terminate unexpectedly.

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