how can I refactor a container to use a predicate method directly?

Question

The snippet below works. However, it's a bit ugly because it uses a static method to wrap a method call to a predicate.

In other words, I would like to replace:

c.remove_if_true( Value::IsOdd );   // static method

with something like

c.remove_if_true( Value::isOdd );   // member method

There should be one fewer level of indirection and hopefully, the resultant code would be clearer.

How do I refactor my code to call isOdd() directly without having to go through a static method wrapper?

However, if this implementation is as clear as I can make this code, also let me know. TIA.

#include <vector>
#include <functional>

template< typename T >
class MyContainer
{
public:
    typedef std::function<bool(const T& t)>   PREDICATE;

public:
    void remove_if_true( PREDICATE predicate )
    {
        // NOTE: use implementation from KennyTM's answer below
    }
private:
    std::vector< T >  m_vec;
};

class Value
{
public:
    Value( int i ) : m_i( i ) { }
    bool isOdd() const { return m_i%2==1; }
    static bool IsOdd( const Value& v ) { return v.isOdd(); }
private:
    int m_i;
};


int main()
{
    MyContainer<Value> c;

    c.remove_if_true( Value::IsOdd );  // would like to replace with Value::isOdd here
}

Solution using KennyTM's Answer

ataylor's suggestion std::mem_fun_ref() required with gcc 4.6.1 and other compilers not completely up-to-date with latest standards

#include <vector>
#include <algorithm>
#include <functional>

template< typename T >
class MyContainer
{
public:
    typedef std::const_mem_fun_ref_t<bool, T>  PREDICATE;

public:
    void remove_if( PREDICATE predicate )
    {
        auto old_end = m_vec.end();
        auto new_end = std::remove_if(m_vec.begin(), old_end, predicate);
        m_vec.erase(new_end, old_end);
    }
private:
    std::vector< T >  m_vec;
};

class Value
{
public:
    Value( int i ) : m_i( i ) { }
    bool isOdd() const { return m_i%2==1; }
private:
    int m_i;
};


int main()
{
    MyContainer<Value> c;

    c.remove_if( std::mem_fun_ref( &Value::isOdd ));
}

Answer 1

c.remove_if_true( std::bind( &Value::isOdd, _1 ) );

Answer 2

c.remove_if_true( std::mem_fn(&Value::isOdd) );

---

BTW, is there any reason you need to avoid std::remove_if ?

void remove_if_true(PREDICATE predicate)
{
    auto old_end = m_vec.end();
    auto new_end = std::remove_if(m_vec.begin(), old_end, predicate);
    m_vec.erase(new_end, old_end);
}

Answer 3

您可以使用std::mem_fn_ref包装isOdd ：

c.remove_if_true( std::mem_fun_ref(&Value::isOdd) );

Answer 4

Best way use lambdas :

c.remove_if_true( [] (const Value & v) { return v.get() % 2 == 0; } );

Or more self-commented :

auto isOdd = [] (const Value & v) { return v.get() % 2 == 0; };
c.remove_if_true( isOdd );