A good strategy is to share the code with your colleage and

inform of your boss " I haved share my code with xxxx. It can integrate the knowledge from both of us and find the effective solution to benefit our products."

As a boss, he would like to see his employees cooperating each other. Remember that always mention contributions from team work instead of yourself.
To move forward your career path, you should position your image as a good team player or leader instead of individual expert.

You should protect yourself in a smart way.