Q_DECLARE_METATYPE a boost :: multi_array

Question

I am trying to pass a multidimensional array, presented as boost :: multi_array, using Qt signals and slots. I tried to declare a meta type using the following code snippet:

Q_DECLARE_METATYPE(boost::multi_array<double, 2>) 

However, I get the following compilation errors (on MSVC 2015):

 path\to\project\metatypes.h(7): error C2976: 'boost::multi_array': too few template arguments ..\..\ml_project\boost-libs\include\boost/multi_array.hpp(111): note: see declaration of 'boost::multi_array' path\to\project\metatypes.h(7): error C2332: 'enum': missing tag name path\to\project\metatypes.h(7): error C2065: 'Defined': undeclared identifier path\to\project\metatypes.h(7): error C2143: syntax error: missing '>' before ';' path\to\project\metatypes.h(7): error C2059: syntax error: '>' path\to\project\metatypes.h(7): error C2976: 'QMetaTypeId': too few template arguments c:\qt\qt-everywhere-opensource-src-5.5.0\qtbase\include\qtcore\../../src/corelib/kernel/qmetatype.h(1576): note: see declaration of 'QMetaTypeId' path\to\project\metatypes.h(7): error C2913: explicit specialization; 'QMetaTypeId' is not a specialization of a class template ..\..\ml_project\boost-libs\include\boost/multi_array.hpp(111): note: see declaration of 'boost::multi_array' ..\..\ml_project\boost-libs\include\boost/multi_array.hpp(111): note: see declaration of 'boost::multi_array' path\to\project\metatypes.h(7): error C2226: syntax error: unexpected type 'quintptr' path\to\project\metatypes.h(7): error C2143: syntax error: missing ')' before ';' path\to\project\metatypes.h(7): error C2143: syntax error: missing ';' before '}' 

Answer 1

The comma between double, 2 parsed as part of the macro definition. The solutions are as follows:

Option number 1

 typedef boost::multi_array<double, 2> my_name; Q_DECLARE_METATYPE( my_name ); 

Option number 2

 #include <boost/utility/identity_type.hpp> Q_DECLARE_METATYPE( BOOST_IDENTITY_TYPE( (boost::multi_array<double, 2>) ) ); 

Option number 3

Handwritten BOOST_IDENTITY_TYPE :

 template <typename T> struct identity_type; template <typename T> struct identity_type<void(T)> { typedef T type; }; #define IDENTITY_TYPE(T) typename identity_type<void T>::type Q_DECLARE_METATYPE( IDENTITY_TYPE( (boost::multi_array<double, 2>) ) ); 

Option number 4

Replace the comma with the preprocessor macro:

 #define COMMA , Q_DECLARE_METATYPE( boost::multi_array<double COMMA 2> ); #undef COMMA