Because SetWindowLong can be used to set a callback function, i.e. a 64-bit pointer - but LONG remains 32 bit on 64-bit Windows. Backward compatibility stipulat

Because SetWindowLong can be used to set a callback function, i.e. a 64-bit pointer - but LONG remains 32 bit on 64-bit Windows. Backward compatibility stipulated the need for a new function name