Item 40. Namespaces, Part 2: Migrating to Namespaces

I l @ ve RuBoard

Difficulty: 4

What's the best way to use C++'s powerful namespace management facilities while avoiding traps and pitfalls? Further, what's the most effective way to initially migrate your existing C++ code to a namespace-aware compiler and library?

You are working on a MLOC (million-lines-of-code) project with more than 1,000 . h and . cpp files. The project team is just upgrading to the latest version of your compiler, which finally both supports namespaces and puts all the standard library features into namespace std (or your compiler already had namespace support, but until now your team has been using legacy pre-namespace headers such as <vector.h> ). Unfortunately, this conformance boon (or header migration) has the side effect of breaking your current build. As always, there is never enough time allocated to do a detailed job. You would like to analyze every source file and write exactly the needed using-declarations in each one, but that's infeasible at this time.

What is the most effective way to deal with this problem and safely migrate your code base to the new (and more standard) environment? Discuss alternatives, and prefer the quickest approach that gets the job done, without compromising future safety and usability. How can you best defer unnecessary (for now) migration work to the future, without increasing the overall migration workload later?

I l @ ve RuBoard