create a new class Foo.
in foo.h declare a public function

bool isBaz(int value) const;

now move cursor onto "isBaz", press Alt+Enter and let QtCreator create the implementation of the function in foo.cpp.
the helper creates the definition

bool Foo::isBaz(int value)
{
}

but without the "const"
now compile - the compiler claims that the prototype for the function does not match any in class Foo.
Add the "const" manually in foo.cpp, and it works.