CppCon 2019

Libraries for C++ are constantly evolving, with new APIs being added, old ones being deprecated and functionality continually changing. In past CppCon talks, I've described in abstract how Google manages this change by applying large-scale changes across our C++ codebase using clang's libTooling infrastructure.

In this talk, we'll put this previous work in practice by demonstrating how we use clang-tidy and clang's libTooling library to improve type safety of time types across Google's 250M lines of C++. Using tools currently open sourced as part of clang-tidy, we'll show how the underlying model of time types allow us to migrate from a collection of integers and floating point types to the much more strongly typed `absl::Time` and `absl::Duration` types representing time instants and intervals. Along the way, we'll discover how this process finds existing bugs and prevents new ones from creeping in.

This "gradual typing" technique is not limited to just Time types, and we'll explore how this can be used to improve pointer ownership deduction and other places where more constraining types eliminate classes of bugs.