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folly
?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.
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.
Folly has an experimental
directory as well. This designation connotes primarily that we feel the API may change heavily over time. This code, typically, is still in heavy use and is well tested.
At the top level Folly uses the classic "stuttering" scheme folly/folly
used by Boost and others. The first directory serves as an installation root of the library (with possible versioning a la folly-1.0/
), and the second is to distinguish the library when including files, e.g. #include <folly/FBString.h>
.
The directory structure is flat (mimicking the namespace structure), i.e. we don't have an elaborate directory hierarchy (it is possible this will change in future versions). The subdirectory experimental
contains files that are used inside folly and possibly at Facebook but not considered stable enough for client use. Your code should not use files in folly/experimental
lest it may break when you update Folly.
The folly/folly/test
subdirectory includes the unittests for all components, usually named ComponentXyzTest.cpp
for each ComponentXyz.*
. The folly/folly/docs
directory contains documentation.
Because of folly's fairly flat structure, the best way to see what's in it is to look at the headers in top level folly/
directory. You can also check the docs
folder for documentation, starting with the overview.
Folly is published on Github at https://github.com/facebook/folly
folly requires gcc 4.9+ and a version of boost compiled with C++14 support.
googletest is required to build and run folly's tests. You can download it from https://github.com/google/googletest/archive/release-1.8.0.tar.gz The following commands can be used to download and install it:
If you have boost, gtest, or other dependencies installed in a non-default location, you can use the CMAKE_INCLUDE_PATH
and CMAKE_LIBRARY_PATH
variables to make CMAKE look also look for header files and libraries in non-standard locations. For example, to also search the directories /alt/include/path1
and /alt/include/path2
for header files and the directories /alt/lib/path1
and /alt/lib/path2
for libraries, you can invoke cmake
as follows:
The following packages are required (feel free to cut and paste the apt-get command below):
If advanced debugging functionality is required, use:
In the folly directory, run:
folly is available as a Formula and releases may be built via brew install folly
.
You may also use folly/build/bootstrap-osx-homebrew.sh
to build against master
:
Install the required packages from MacPorts:
Download and install double-conversion:
Download and install folly with the parameters listed below:
folly is available in Vcpkg and releases may be built via vcpkg install folly:x64-windows
.
You may also use vcpkg install folly:x64-windows --head
to build against master
.
double-conversion (https://github.com/google/double-conversion)
Download and build double-conversion. You may need to tell cmake where to find it.
[double-conversion/] ln -s src double-conversion
[folly/] mkdir build && cd build
[folly/build/] cmake "-DCMAKE_INCLUDE_PATH=$DOUBLE_CONVERSION_HOME/include" "-DCMAKE_LIBRARY_PATH=$DOUBLE_CONVERSION_HOME/lib" ..
[folly/build/] make
additional platform specific dependencies:
Fedora >= 21 64-bit (last tested on Fedora 28 64-bit)
Optional