Re: passing function object pointer to for_each argument

In article <1190880439.757760.323040@n39g2000hsh.googlegroups.com>,
 hongseok.yoon@gmail.com wrote:


for_each handles it's functor by value. In the second case, the value of
*b is copied into a test_a object that is stored inside the for_each
algorithm. To fix it, you need to add a level of indirection.

class test_t {
public:
   virtual void test(int) = 0;
};

class test_a : public test_t {
   void test(int) {
      cout << "test_a::_test()\n";
   }
};

class test_b : public test_t {
   void test(int) {
      cout << "test_b::_test()\n";
   }
};

int main()
{
   auto_ptr<test_t> a( new test_a );
   auto_ptr<test_t> b( new test_b );
   
   vector<int> v;
   v.push_back( 1 );
   
   for_each( v.begin(), v.end(),
      bind1st( mem_fun( &test_t::test ), a.get() ) );
   for_each( v.begin(), v.end(),
      bind1st( mem_fun( &test_t::test ), b.get() ) );
   
   return 0;
}

In the above code, I modified the test function somewhat so I could use
some of the functional parts of the language to build a wrapper, but you
can build one manually if you want:

class wrapper {
   test_t* test;
public:
   wrapper( test_t* t ): test( t ) { }
   void operator()( int i ) {
      test->test(); // assumes that '_test' takes no args like your
                    // example.
   }
};

for_each( v.begin(), v.end(), wrapper( a.get() ) );

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