I need to migrate an ancient codebase to support c++17. This means removing auto_ptr, unary_function etc. I’ve already removed several instances of unary_function successfully but this one is a puzzler.
Here are the prerequisites: Traits macro, RemoveConstRef template.
<code>template <class T>
struct RemoveConstRef {
typedef T type;
};
#define FPTRAITS_BASIC( _type, _paramType )
template <>
struct Traits<_type> {
typedef _type param_type;
typedef _type return_type;
static int fp_param_type() { return _paramType; }
static int fp_return_type() { return _paramType; }
static param_type get_parameter( FPValue& fpValue ) { return FP_FIELD( _paramType, fpValue ); }
static void get_return_value( FPValue& fpOutValue, return_type val ) {
return fpOutValue.LoadPtr( _paramType, FP_RSLT( _paramType, val ) );
}
};
FPTRAITS_BASIC( int, TYPE_INT )
FPTRAITS_BASIC( float, TYPE_FLOAT )
...
</code>
<code>template <class T>
struct RemoveConstRef {
typedef T type;
};
#define FPTRAITS_BASIC( _type, _paramType )
template <>
struct Traits<_type> {
typedef _type param_type;
typedef _type return_type;
static int fp_param_type() { return _paramType; }
static int fp_return_type() { return _paramType; }
static param_type get_parameter( FPValue& fpValue ) { return FP_FIELD( _paramType, fpValue ); }
static void get_return_value( FPValue& fpOutValue, return_type val ) {
return fpOutValue.LoadPtr( _paramType, FP_RSLT( _paramType, val ) );
}
};
FPTRAITS_BASIC( int, TYPE_INT )
FPTRAITS_BASIC( float, TYPE_FLOAT )
...
</code>
template <class T>
struct RemoveConstRef {
typedef T type;
};
#define FPTRAITS_BASIC( _type, _paramType )
template <>
struct Traits<_type> {
typedef _type param_type;
typedef _type return_type;
static int fp_param_type() { return _paramType; }
static int fp_return_type() { return _paramType; }
static param_type get_parameter( FPValue& fpValue ) { return FP_FIELD( _paramType, fpValue ); }
static void get_return_value( FPValue& fpOutValue, return_type val ) {
return fpOutValue.LoadPtr( _paramType, FP_RSLT( _paramType, val ) );
}
};
FPTRAITS_BASIC( int, TYPE_INT )
FPTRAITS_BASIC( float, TYPE_FLOAT )
...
Original implimenation
<code>
template <class T, int Index>
struct get_parameter : public std::unary_function< FPParams*, typename Traits< typename RemoveConstRef<T>::type >::param_type >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
</code>
<code>
template <class T, int Index>
struct get_parameter : public std::unary_function< FPParams*, typename Traits< typename RemoveConstRef<T>::type >::param_type >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
</code>
template <class T, int Index>
struct get_parameter : public std::unary_function< FPParams*, typename Traits< typename RemoveConstRef<T>::type >::param_type >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
c++17 attempt
<code> template <class T, int Index>
struct get_parameter : public std::function<typename Traits< typename RemoveConstRef<T>::type >::param_type(FPParams*) >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
</code>
<code> template <class T, int Index>
struct get_parameter : public std::function<typename Traits< typename RemoveConstRef<T>::type >::param_type(FPParams*) >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
</code>
template <class T, int Index>
struct get_parameter : public std::function<typename Traits< typename RemoveConstRef<T>::type >::param_type(FPParams*) >{
inline result_type operator()( FPParams* p ) const {
return Traits< typename RemoveConstRef<T>::type >::get_parameter( p->params[Index] );
}
};
These are the compiler errors:
error C2143: syntax error: missing ‘;’ before ‘(‘ at the operator keyword
2
I think you’re missing the point of std::unary_function versus std::function. The two are entirely unrelated, and it makes no sense to rewrite get_parameter like you did.
std::unary_function provided argument_type and result_type. With new C++11 features like auto, those typedefs are no longer necessary. Just remove it entirely. The return type of operator() can simply become auto.
3