What C++ templates issue is going on with this error?

Question

Running gcc v3.4.6 on the Botan v1.8.8 I get the following compile time error building my application after successfully building Botan and running its self test:

../../src/Botan-1.8.8/build/include/botan/secmem.h: In member function `Botan::MemoryVector<T>& Botan::MemoryVector<T>::operator=(const Botan::MemoryRegion<T>&)':
../../src/Botan-1.8.8/build/include/botan/secmem.h:310: error: missing template arguments before '(' token

What is this compiler error telling me? Here is a snippet of secmem.h that includes line 310:

[...]
/**
* This class represents variable length buffers that do not
* make use of memory locking.
*/
template<typename T>
class MemoryVector : public MemoryRegion<T>
   {
   public:
      /**
      * Copy the contents of another buffer into this buffer.
      * @param in the buffer to copy the contents from
      * @return a reference to *this
      */
      MemoryVector<T>& operator=(const MemoryRegion<T>& in)
         { if(this != &in) set(in); return (*this); }  // This is line 310!
[...]

Answer 1

Change it to this:

{ if(this != &in) this->set(in); return (*this); } 

I suspect that the set function is defined in the base-class? Unqualified names are not looked up in a base class that depends on a template parameter. So in this case, the name set is probably associated with the std::set template which requires template arguments.

If you qualify the name with this->, the compiler is explicitly told to look into the scope of the class, and includes dependent base classes in that lookup.