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Struct template has_env_var

boost::proto::functional::has_env_var — A unary boolean PolymorphicFunctionObject used for determining whether a particular transform environment has a value associated with a particular key.


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

template<typename Key> 
struct has_env_var :  proto::callable {
  // member classes/structs/unions
  template<typename Sig> 
  struct result {
    // types
    typedef see-below type;

  // public member functions
  template<typename Env> see-below operator()(Env const &) const;


has_env_var public member functions

  1. template<typename Env> see-below operator()(Env const & e) const;

    This function behaves as follows: