'this' argument to member function 'select' has type 'const SelectParam', but function is not marked const

Question

I\'m trying to call a function on a polymorphic item. But I get the following error message at compile time:

\'this\' argument to member

Answer 1

You need to explicitly tell the compiler that your function will not modify any members:

bool const select(Tuple const & tup) const {

Answer 2

Indeed, you cannot call a non-const method a const object. But you also cannot call a non-const method through a pointer or reference to a const object (regardless of whether the referred-to object is const or not).

This means that this:

const SelectParam* ptr = whatever();
ptr->select(someTuple);

is ill-formed.

In your case, you've declared a pointer to a const SelectParam here on this line:

for (const SelectParam* p: selectionParams) {

Simply remove the const and it should work :-)

On the other hand, if select is never meant to modify the object, simply mark it as const:

virtual const bool select( Tuple const & t) const = 0;

And your code should also work.