facebook/folly

Folly (acronymed loosely after Facebook Open Source Library) is a library of C++17 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.

Folly is a collection of relatively independent components, some as simple as a few symbols. There is no restriction on internal dependencies, meaning that a given folly module may use any other folly components.

All symbols are defined in the top-level namespace folly, except of course macros. Macro names are ALL_UPPERCASE and should be prefixed with FOLLY_. Namespace folly defines other internal namespaces such as internal or detail. User code should not depend on symbols in those namespaces.