CODEWITHSUNDEEP
c++templatesboost
xiaodong
xiaodong

Reputation: 1012

boost check if the type belong to a list of given types

I have the following problem. In the template, I want to check if the type is one of the given types.

Code description:

tempalte <typename T>
class foo
{
public:
//BOOST_STATIC_ASSERT(T is one of int, long, long long, double ....);
//boost::is_scalar doesn't fill my requirements since I need 
//to provide my own list of types
};

I know how to do it using the template specification, but this way is tedious. 

   template <typename T>
    class ValidateType
    {
        static const bool valid = false;
    };

    template <>
    class ValidateType<int>
    {
        static const bool valid = true;
    }

    //repeat for every wanted type

Is there elegant way?

Upvotes: 2

Views: 1086

Answers (2)

gTcV
gTcV

Reputation: 2504

This works:

#include <boost/mpl/set.hpp>
#include <boost/mpl/assert.hpp>

typedef boost::mpl::set<int, long, long long, double, ...> allowed_types;
BOOST_MPL_ASSERT((boost::mpl::has_key<allowed_types, int>));  // Compiles
BOOST_MPL_ASSERT((boost::mpl::has_key<allowed_types, char>)); // Causes compile-time error

Upvotes: 4

Joseph Mansfield
Joseph Mansfield

Reputation: 110658

You can use an MPL vector (which is a vector of types) with the contains algorithm:

typedef vector<int, long, long long, double> types;
BOOST_MPL_ASSERT(( contains<types, T> ));

Upvotes: 1

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