Comparison tricks in C++

Question

A class:

class foo{
public:
    int data;
};

Now I want to add a method to this class, to do some comparison, to see if its data is equal to on

Answer 1

The answers using std::initializer_list are fine, but I want to add one more possible solution which is exactly what you where trying with that C variadic in a type-safe and modern way: Using C++11 variadic templates:

template
bool any_equal( const foo& f , NUMBERS&&... numbers )
{
    auto unpacked = { numbers... };

    return std::find( std::begin( unpacked ) , std::end( unpacked ) , f.data ) 
           != std::end( unpacked );
};

Of course this only works if all values passed are of the same type. If not the initializer list unpacked cannot be deduced nor initialized.

Then:

bool equals = any_equal( f , 1,2,3,4,5 );

EDIT: Here is a are_same metafunction to ensure that all the numbers passed are of the same type:

template
struct are_same : public and_op::value...>
{};

Where and_op performs n-ary logical and:

template
struct and_op : public std::integral_constant::value>
{};

template<>
struct and_op<> : public std::true_type
{};

This makes possible to force the usage of numbers of the same type in a simple way:

template
bool any_equal( const foo& f , NUMBERS&&... numbers )
{
    static_assert( all_same::value , 
                   "ERROR: You should use numbers of the same type" );


    auto unpacked = { numbers... };

    return std::find( std::begin( unpacked ) , std::end( unpacked ) , f.data ) 
           != std::end( unpacked );
};