<s>
Buck	B-Application
is	O
a	O
multi-language	O
build	B-Application
system	I-Application
developed	O
and	O
used	O
by	O
Meta	O
Platforms	O
,	O
Inc	O
.	O
</s>
<s>
It	O
was	O
designed	O
for	O
building	O
small	O
,	O
reusable	O
modules	O
consisting	O
of	O
code	O
and	O
resources	O
within	O
a	O
monorepo	B-General_Concept
.	O
</s>
<s>
It	O
supports	O
many	O
programming	O
languages	O
,	O
including	O
C++	B-Language
,	O
Swift	B-Application
,	O
Shell	B-Operating_System
,	O
Java	B-Language
,	O
Kotlin	B-Language
,	O
Python	B-Language
,	O
Lua	B-Language
,	O
OCaml	B-Language
,	O
Rust	B-Application
and	O
Go	B-Application
.	O
</s>
<s>
It	O
can	O
produce	O
binary	O
outputs	O
for	O
a	O
variety	O
of	O
target	O
platforms	O
including	O
IOS	B-Application
,	O
Android	B-Application
,	O
.NET	B-Application
and	O
Java	B-Language
VM	I-Language
runtimes	B-Device
.	O
</s>
<s>
Buck1	O
was	O
licensed	O
under	O
the	O
Apache	B-Application
License	I-Application
2.0	I-Application
,	O
while	O
Buck2	O
is	O
licensed	O
under	O
either	O
MIT ]	O
OR	O
Apache	B-Application
License	I-Application
2.0	I-Application
.	O
</s>
<s>
Buck	B-Application
requires	O
the	O
explicit	O
declaration	O
of	O
dependencies	O
.	O
</s>
<s>
Because	O
all	O
dependencies	O
are	O
explicit	O
and	O
Buck	B-Application
has	O
a	O
directed	O
acyclic	O
graph	O
of	O
all	O
source	O
files	O
and	O
build	O
targets	O
,	O
Buck	B-Application
can	O
perform	O
incremental	O
recompilation	O
,	O
only	O
rebuilding	O
targets	O
downstream	O
of	O
files	O
that	O
have	O
changed	O
.	O
</s>
<s>
Buck	B-Application
computes	O
a	O
key	O
for	O
each	O
target	O
that	O
is	O
a	O
hash	O
of	O
the	O
contents	O
of	O
the	O
files	O
it	O
depends	O
on	O
.	O
</s>
<s>
One	O
of	O
the	O
largest	O
changes	O
from	O
Buck1	O
is	O
that	O
the	O
core	O
is	O
written	O
in	O
Rust	B-Application
instead	O
of	O
Java	B-Language
,	O
and	O
rules	O
are	O
written	O
outside	O
the	O
core	O
in	O
Starlark	O
(	O
the	O
language	O
created	O
for	O
the	O
Bazel	O
build	B-Application
system	I-Application
)	O
.	O
</s>
