Boost C++ Libraries

...one of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

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Getting started

How to use
Example with Boost.Any
Example with Boost.Variant

boost::typeindex::type_info is a drop-in replacement for std::type_info and boost::typeindex::type_index is a drop-in replacement for std::type_index. Unlike Standard Library versions those classes can work without RTTI.

type_index provides the full set of comparison operators, hashing functions and ostream operators, so it can be used with any container class.

To start using Boost.TypeIndex:

Replace this:

With the following:

More Info

#include <typeinfo>
#include <typeindex>
#include <boost/type_index.hpp>

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std::type_index
boost::typeindex::type_index

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typeid(T)
typeid(T).name() // not human readable
typeid(variable)
boost::typeindex::type_id<T>()
boost::typeindex::type_id<T>().pretty_name() // human readable
boost::typeindex::type_id_runtime(variable)

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// attempt to save const, volatile, reference
typeid(please_save_modifiers<T>)
// cvr = const, volatile, reference
boost::typeindex::type_id_with_cvr<T>()

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// when reference to `std::type_info` is required
const std::type_info& v1 = typeid(int);

// other cases
const std::type_info* v2 = &typeid(int);
const boost::typeindex::type_info& v1
    = boost::typeindex::type_id<int>().type_info();

boost::typeindex::type_index v2
    = boost::typeindex::type_id<int>();

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If you are using type_id_runtime() methods and RTTI is disabled, make sure that classes that are passed to type_id_runtime() are marked with BOOST_TYPE_INDEX_REGISTER_CLASS macro.

Here is how TypeIndex could be used in boost/any.hpp:

Before

With TypeIndex

#include <typeinfo>
#include <boost/type_index.hpp>
virtual const std::type_info & type() const BOOST_NOEXCEPT
{
    // requires RTTI
    return typeid(ValueType);
}
virtual const boost::typeindex::type_info & type() const BOOST_NOEXCEPT
{
    // now works even with RTTI disabled
    return boost::typeindex::type_id<ValueType>().type_info();
}

Here is how TypeIndex could be used in boost/variant/variant.hpp:

Before

With TypeIndex

#if !defined(BOOST_NO_TYPEID)
#include <typeinfo> // for typeid, std::type_info
#endif // BOOST_NO_TYPEID
#include <boost/type_index.hpp>
#if !defined(BOOST_NO_TYPEID)

class reflect
    : public static_visitor<const std::type_info&>
{
public: // visitor interfaces

    template <typename T>
    const std::type_info& operator()(const T&) const BOOST_NOEXCEPT
    {
        return typeid(T);
    }

};

#endif // BOOST_NO_TYPEID
class reflect
    : public static_visitor<const boost::typeindex::type_info&>
{
public: // visitor interfaces

    template <typename T>
    const boost::typeindex::type_info& operator()(const T&) const BOOST_NOEXCEPT
    {
        return boost::typeindex::type_id<T>().type_info();
    }

};
#if !defined(BOOST_NO_TYPEID)
    const std::type_info& type() const
    {
        detail::variant::reflect visitor;
        return this->apply_visitor(visitor);
    }
#endif
const boost::typeindex::type_info& type() const
{
    detail::variant::reflect visitor;
    return this->apply_visitor(visitor);
}

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