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Struct template value

boost::xpressive::value — value<> is a lazy wrapper for a value that can be used in xpressive semantic actions.

Synopsis

// In header: <boost/xpressive/regex_actions.hpp>

template<typename T> 
struct value :
  public proto::extends< proto::terminal< T >::type, value< T > >
{
  // construct/copy/destruct
  value();
  explicit value(T const &);

  // public member functions
  T & get();
  T const & get() const;
};

Description

Below is an example that shows where value<> is useful.

sregex good_voodoo(boost::shared_ptr<int> pi)
{
    using namespace boost::xpressive;
    // Use val() to hold the shared_ptr by value:
    sregex rex = +( _d [ ++*val(pi) ] >> '!' );
    // OK, rex holds a reference count to the integer.
    return rex;
}

In the above code, xpressive::val() is a function that returns a value<> object. Had val() not been used here, the operation ++*pi would have been evaluated eagerly once, instead of lazily when the regex match happens.

Template Parameters

  1. typename T

    The type of the value to store.

value public construct/copy/destruct

  1. value();
    Store a default-constructed T.
  2. explicit value(T const & t);
    Store a copy of t.

    Parameters:

    t

    The initial value.

value public member functions

  1. T & get();

    This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

  2. T const & get() const;
    Fetch the stored value.

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