| Home | Libraries | People | FAQ | More

## Class template param

boost::type_erasure::param — A wrapper to help with overload resolution for functions operating on an any.

## Synopsis

    // In header: <boost/type_erasure/param.hpp>

    template<typename Concept, typename T>
    class param {
    public:
      // construct/copy/destruct
      template<typename U> param(any< Concept, U > &);
      template<typename U> param(const any< Concept, U > &);
      template<typename U> param(any< Concept, U > &&);

      // public member functions
      any< Concept, T > get() const;
    };

## Description

The template arguments are interpreted in the same way as any.

A parameter of type param can be initialized with an any that has the same `Concept` and base placeholder when there exists a corresponding standard conversion for the placeholder. A conversion sequence from any<C, P> to param<C, P1> is a better conversion sequence than any<C, P> to param<C, P2> iff the corresponding placeholder standard conversion sequence from P to P1 is a better conversion sequence than P to P2.

| Note
Overloading based on cv-qualifiers and rvalue-ness is only supported in C++11. In C++03, all conversion sequences from any to param have the same rank.

Example:

    void f(param<C, _a&>);
    void f(param<C, const _a&>);
    void g(param<C, const _a&>);
    void g(param<C, _a&&>);

    any<C, _a> a;
    f(any<C, _a>()); // calls void f(param<C, const _a&>);
    f(a);            // calls void f(param<C, _a&>); (ambiguous in C++03)
    g(any<C, _a>()); // calls void g(param<C, _a&&>); (ambiguous in C++03)
    g(a);            // calls void g(param<C, const _a&>);

### `param` public construct/copy/destruct

1.     template<typename U> param(any< Concept, U > & a);

2.     template<typename U> param(const any< Concept, U > & a);

3.     template<typename U> param(any< Concept, U > && a);

### `param` public member functions

1.     any< Concept, T > get() const;

   Returns the stored `any`.