...one of the most highly
regarded and expertly designed C++ library projects in the
world.
— Herb Sutter and Andrei
Alexandrescu, C++
Coding Standards
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 typedefsee-below
type; }; // public member functions template<typename Env>see-below
operator()(Env const &) const; };
has_env_var
public member functionstemplate<typename Env> see-below
operator()(Env const & e) const;
This function behaves as follows:
proto::is_env<Env>::value
is true
:
e[Key()]
returns an instance of
proto::key_not_found
, return
mpl::false_
. See proto::env::operator[]
for more information.
mpl::true_
.
Key
is proto::data_type
,
return mpl::true_
.
mpl::false_
.