Folly

C++ library developed and used at Facebook

Folly acronymed loosely after Facebook Open Source Library is a library of C++14 components designed with practicality and efficiency in mind. Folly contains a variety of core library components used extensively at Facebook. In particular, it’s often a dependency of Facebook’s other open source C++ efforts and place where those projects can share code.

It complements as opposed to competing against offerings such as Boost and of course std. In fact, we embark on defining our own component only when something we need is either not available, or does not meet the needed performance profile. We endeavor to remove things from folly if or when std or Boost obsoletes them.

Performance concerns permeate much of Folly, sometimes leading to designs that are more idiosyncratic than they would otherwise be see e.g. PackedSyncPtr.h, SmallLocks.h. Good performance at large scale is a unifying theme in all of Folly.