E.8 Handle Template Adaptors

IceUtil provides adaptors that support use of smart pointers with STL algorithms. Each template function returns a corresponding function object that is for use by an STL algorithm. The adaptors are defined in the header IceUtil/Functional.h.

Here is a list of the adaptors:

memFun
memFun1
voidMemFun
voidMemFun1

secondMemFun
secondMemFun1
secondVoidMemFun
secondVoidMemFun1

constMemFun
constMemFun1
constVoidMemFun
constVoidMemFun1

secondConstMemFun
secondConstMemFun1
secondConstVoidMemFun
secondConstVoidMemFun1

As you can see, the adaptors are in two groups. The first group operates on non-const smart pointers, whereas the second group operates on const smart pointers (for example, on smart pointers declared as const MyClassPtr).

Each group is further divided into two sub-groups. The adaptors in the first group operate on the target of a smart pointer, whereas the second<name> adapters operate on the second element of a pair, where that element is a smart pointer.

Each of the four sub-groups contains four adaptors:

• memFun

This adaptor is used for member functions that return a value and do not accept an argument. For example:

class MyClass : public IceUtil::Shared {
public:
    MyClass(int i) : _i(i) {}
    int getVal() { return _i; }
private:
    int _i;
};

typedef IceUtil::Handle<MyClass> MyClassPtr;

// ...

vector<MyClassPtr> mcp;
mcp.push_back(new MyClass(42));
mcp.push_back(new MyClass(99));

transform(mcp.begin(), mcp.end(),
          ostream_iterator<int>(cout, " "),
          IceUtil::memFun(&MyClass::getVal));
cout << endl;

This code invokes the member function getVal on each instance that is pointed at by smart pointers in the vector mcp and prints the return value of getVal on cout, separated by spaces. The output from this code is:

42 99

• memFun1

This adaptor is used for member functions that return a value and accept a single argument. For example:

class MyClass : public IceUtil::Shared {
public:
    MyClass(int i) : _i(i) {}
    int plus(int v) { return _i + v; }
private:
    int _i;
};

typedef IceUtil::Handle<MyClass> MyClassPtr;

// ...

vector<MyClassPtr> mcp;
mcp.push_back(new MyClass(2));
mcp.push_back(new MyClass(4));
mcp.push_back(new MyClass(6));

int A[3] = { 5, 7, 9 };
transform(mcp.begin(), mcp.end(), A,
          ostream_iterator<int>(cout, " "),
          IceUtil::memFun1(&MyClass::plus));
cout << endl;

This code invokes the member function plus on each instance that is pointed at by smart pointers in the vector mcp and prints the return value of a call to plus on cout, separated by spaces. The calls to plus are successively passed the values stored in the array A. The output from this code is:

7 11 15

• voidMemFun

This adaptor is used for member functions that do not return a value and do not accept an argument. For example:

class MyClass : public IceUtil::Shared {
public:
    MyClass(int i) : _i(i) {}
    void print() { cout << _i << endl; }
private:
    int _i;
};

typedef IceUtil::Handle<MyClass> MyClassPtr;

// ...

vector<MyClassPtr> mcp;
mcp.push_back(new MyClass(2));
mcp.push_back(new MyClass(4));
mcp.push_back(new MyClass(6));

for_each(mcp.begin(), mcp.end(),
         IceUtil::voidMemFun(&MyClass::print));

This code invokes the member function print on each instance that is pointed at by smart pointers in the vector mcp. The output from this code is:

2
4
6

• voidMemFun1

This adaptor is used for member functions that do not return a value and accept a single argument. For example:

class MyClass : public IceUtil::Shared {
public:
    MyClass(int i) : _i(i) {}
    void printPlus(int v) { cout << _i + v << endl; }
private:
    int _i;
};

typedef IceUtil::Handle<MyClass> MyClassPtr;

vector<MyClassPtr> mcp;
mcp.push_back(new MyClass(2));
mcp.push_back(new MyClass(4));
mcp.push_back(new MyClass(6));

for_each(
    mcp.begin(), mcp.end(),
    bind2nd(IceUtil::voidMemFun1(&MyClass::printPlus), 3));

This code invokes the member function printPlus on each instance that is pointed at by smart pointers in the vector mcp. The output from this code is:

5
7
9

As mentioned on page 1761, the second<name> versions of the adaptors operate on the second element of a std::pair<T1, T2>, where T2 must be a smart pointer. Most commonly, these adaptors are used to apply an algorithm to each lookup value of a map or multi-map. Here is an example:

class MyClass : public IceUtil::Shared {
public:
    MyClass(int i) : _i(i) {}
    int plus(int v) { return _i + v; }
private:
    int _i;
};

typedef IceUtil::Handle<MyClass> MyClassPtr;

// ...

map<string, MyClassPtr> m;
m["two"] = new MyClass(2);
m["four"] = new MyClass(4);
m["six"] = new MyClass(6);

int A[3] = { 5, 7, 9 };
transform(
    m.begin(), m.end(), A,
    ostream_iterator<int>(cout, " "),
    IceUtil::secondMemFun1<int, string, MyClass>(&MyClass::plus));

This code invokes the plus member function on the class instance denoted by the second smart pointer member of each pair in the dictionary m. The output from this code is:

9 13 11

Note that secondMemFun1 is a template that requires three arguments: the return type of the member function to be invoked, the key type of the dictionary, and the type of the class that is pointed at by the smart pointer.

In general, the second<name> adaptors require the following template arguments:

secondMemFun<R, K, T>
secondMemFun1<R, K, T>
secondVoidMemFun<K, T>
secondVoidMemFun<K, T>

where R is the return type of the member function, K is the type of the first member of the pair, and T is the class that contains the member function.