type/value mismatch at argument with Template

Question

I am writing some c++ template code to replace if-else conditions in present source. Here, I am deriving Helper data type based on two conditions, 1. isAdvice 2. SimpleOrComplex

See below template code:

template<bool isAdvice, class SH, class CH>
class IfThenElse;

template<class SH, class CH>
class IfThenElse<true, SH, CH>
{
    public:
    typedef SH Helper;
};

template<class SH, class CH>
class IfThenElse<false, SH, CH>
{
    public:
    typedef CH Helper;
};

template <bool isAdvice, bool SimpleOrComplex>
class DeriveHelper
{
    public:
        typedef typename IfThenElse<isAdvice,
                 IfThenElse<SimpleOrComplex, SimpleHelper, ComplexHelper>::Helper,
                 IfThenElse<SimpleOrComplex, SimpleNoAdvHelper, ComplexNoAdvHelper>::Helper>::Helper DerivedHelper;


};

However, Getting this error at compilation:

template.cpp:135: error: type/value mismatch at argument 2 in template parameter list for 'template<bool isTradeAdvice, class SH, class GH> struct IfThenElse'
template.cpp:135: error:   expected a type, got 'IfThenElse::Helper'
template.cpp:135: error: type/value mismatch at argument 3 in template parameter list for 'template<bool isTradeAdvice, class SH, class GH> struct IfThenElse'
template.cpp:135: error:   expected a type, got 'IfThenElse::Helper'

Can someone please suggest the reason?

Your `IfThenElse` just duplicates [`std::conditional`](http://en.cppreference.com/w/cpp/types/conditional). — Angew is no longer proud of SO, Oct 13 '14 at 08:20

score 4 · Accepted Answer · answered Oct 13 '14 at 07:48

You should prepend a typename keyword for the two template type parameters IfThenElse as you did for the first one

template <bool isAdvice, bool SimpleOrComplex>
class DeriveHelper
{
public:
    typedef typename IfThenElse<isAdvice,
                 typename IfThenElse<SimpleOrComplex, SimpleHelper, ComplexHelper>::Helper,
                 ^^^^^^^^
                 typename IfThenElse<SimpleOrComplex, SimpleNoAdvHelper, ComplexNoAdvHelper>::Helper>::Helper DerivedHelper;
                 ^^^^^^^^
};

type/value mismatch at argument with Template

1 Answers1