Struct template env_var

Boost C++ Libraries

Struct template env_var

boost::proto::functional::env_var — A unary PolymorphicFunctionObject used for fetching the value associated with a particular key in a transform environment.

Synopsis

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

template<typename Key> 
struct 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;
};

Description

`env_var` public member functions

```
template<typename Env> see-below operator()(Env const & e) const;
```
This function behaves as follows:
- If Key is proto::data_type:
  - If proto::is_env<Env>::value is true, return e[proto::data].
  - Otherwise, return e.
- Otherwise, return e[Key()].
See proto::env::operator[] for additional information.