C++Now 2019

Class Template Argument Deduction (CTAD), introduced in C++17, is a useful feature that allows us to write cleaner and shorter code by omitting class template arguments. Unfortunately, the actual language rules behind CTAD are quite complex, and there are many pitfalls. CTAD sometimes deduces unexpected template arguments, and often just doesn’t work at all on certain classes, even if most users would expect that it should.

This talk summarises the actual language rules behind CTAD and its most annoying flaws and pitfalls. We will then talk about how the upcoming C++20 standard will remove some of those flaws, leading to better and safer CTAD that is easier to use.