The medium answer length answer is: learning some 'pure' OOPLs may *hurt* rather than help.
The long answer is: read the previous questions on the difference between C++ and Smalltalk (the usual 'pure' OOPL being discussed; 'pure' means everything is an object of some class; 'hybrid' [like C++] means things like int, char, and float are not instances of a class, hence aren't subclassable).
The 'purity' of the OOPL doesn't make the transition to C++ any more or less difficult; it is the weak typing and improper inheritance that is so hard to get. I've taught numerous people C++ with a Smalltalk background, and they usually have just as hard a time as those who've never seen inheritance before. In fact, my personal observation is that those with extensive experience with a weakly typed OOPL (usually but not always Smalltalk) have a *harder* time, since it's harder to *unlearn* habits than it is to learn the statically typed way from the beginning.
