Hi Robert, It is great to see this library getting into Boost. It fills an important gap, but it is only after a long while that I realized that, because the introductory part of the documentation does not stress it enough, and in fact it misled me a bit. My understanding is that safe<int> represents a high level abstraction of an integral number from mathematics: unlike raw type int, which represents a set of allowed operations on the underlying processor. You could say that raw type 'int' is only needed to efficiently implement higher level abstractions, like BigInt or safe<int> -- the two only differ in trade-offs between efficiency and the range of values they can represent. I was missing this in the introduction. Instead I got a somewhat negative impression that the goal of the library is to turn any UB into throwing exceptions (and thereby prevent any UB-based static analysis from detecting programmer errors). I would like to see the library in Boost, although I must admit the other parts do not sound that compelling as safe<int>. Regards, &rzej