boost::proto::protect< PrimitiveTransform > Struct Template Reference

A PrimitiveTransform which prevents another PrimitiveTransform from being applied in an ObjectTransform. More...

#include <make.hpp>

Inheritance diagram for boost::proto::protect< PrimitiveTransform >:

Collaboration diagram for boost::proto::protect< PrimitiveTransform >:

Classes
struct	impl

Public Types
typedef protect < PrimitiveTransform >	transform_type

Public Member Functions
	BOOST_PROTO_CALLABLE () typedef X proto_is_transform_
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &)> ::result_type	operator() (Expr &&e) const
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &, State const &)> ::result_type	operator() (Expr &&e, State &&s) const
BOOST_FORCEINLINE boost::proto::detail::apply_transform < transform_type(Expr const &, State const &, Data const &)> ::result_type	operator() (Expr &&e, State &&s, Data &&d) const

Detailed Description

template<typename PrimitiveTransform>
struct boost::proto::protect< PrimitiveTransform >

A PrimitiveTransform which prevents another PrimitiveTransform from being applied in an ObjectTransform.

When building higher order transforms with make<> or lazy<>, you sometimes would like to build types that are parameterized with Proto transforms. In such lambda-style transforms, Proto will unhelpfully find all nested transforms and apply them, even if you don't want them to be applied. Consider the following transform, which will replace the _ in Bar<_>() with proto::terminal<int>::type:

template<typename T>
struct Bar
{};

struct Foo
  : proto::when<_, Bar<_>() >
{};

proto::terminal<int>::type i = {0};

int main()
{
    Foo()(i);
    std::cout << typeid(Foo()(i)).name() << std::endl;
}

If you actually wanted to default-construct an object of type Bar<_>, you would have to protect the _ to prevent it from being applied. You can use proto::protect<> as follows:

// OK: replace anything with Bar<_>()
struct Foo
  : proto::when<_, Bar<protect<_> >() >
{};

Member Typedef Documentation

typedef protect< PrimitiveTransform > boost::proto::transform< protect< PrimitiveTransform > , X >::transform_type

inherited

Member Function Documentation

boost::proto::transform< protect< PrimitiveTransform > , X >::BOOST_PROTO_CALLABLE ( )

inherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &, State const &, Data const &)>::result_type boost::proto::transform< protect< PrimitiveTransform > , X >::operator() ( Expr &&  e, State &&  s, Data &&  d  ) const

inlineinherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &, State const &)>::result_type boost::proto::transform< protect< PrimitiveTransform > , X >::operator() ( Expr &&  e, State &&  s  ) const

inlineinherited

BOOST_FORCEINLINE boost::proto::detail::apply_transform<transform_type(Expr const &)>::result_type boost::proto::transform< protect< PrimitiveTransform > , X >::operator() ( Expr &&  e ) const

inlineinherited

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The documentation for this struct was generated from the following file:

• boost_1_57_0/boost/proto/proto_fwd.hpp