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Struct template lazy

boost::proto::lazy — A PrimitiveTransform that uses proto::make<> to build a CallableTransform, and then uses proto::call<> to apply it.


// In header: <boost/proto/transform/lazy.hpp>

template<typename T> 
struct lazy :  proto::transform< lazy<T> > {
  template<typename Expr, typename State, typename Data> 
  struct impl :  proto::transform_impl<Expr, State, Data> {
    // types
    typedef see-below result_type;

    // public member functions
    result_type operator()(typename impl::expr_param, 
                           typename impl::state_param, 
                           typename impl::data_param) const;


proto::lazy<> is useful as a higher-order transform, when the transform to be applied depends on the current state of the transformation. The invocation of the proto::make<> transform evaluates any nested transforms, and the resulting type is treated as a CallableTransform, which is evaluated with proto::call<>.

For the full description of the behavior of the proto::lazy<> transform, see the documentation for the nested proto::lazy::impl<> class template.