In C++ you are supposed to declare functions before you can use them. In your code integrate
is not declared before the point of the first call to integrate
. The same applies to sum
. Hence the error. Either reorder your definitions so that function definition precedes the first call to that function, or introduce a [forward] non-defining declaration for each function.
Additionally, defining external non-inline functions in header files in a no-no in C++. Your definitions of SkewNormalEvalutatable::SkewNormalEvalutatable
, getSkewNormal
, integrate
etc. have no business being in header file.
Also SkewNormalEvalutatable e();
declaration in C++ declares a function e
, not an object e
as you seem to assume. The simple SkewNormalEvalutatable e;
will declare an object initialized by default constructor.
Also, you receive the last parameter of integrate
(and of sum
) by value as an object of Evaluatable
type. That means that attempting to pass SkewNormalEvalutatable
as last argument of integrate
will result in SkewNormalEvalutatable
getting sliced to Evaluatable
. Polymorphism won’t work because of that. If you want polymorphic behavior, you have to receive this parameter by reference or by pointer, but not by value.